Dillander (edited to add: and Dawn!) guessed correctly. The pattern I shamelessly copied is Kwik Sew 3790, although that Burda is very similar. I think I like the KS better though. But that's just my 2 cents.
The fabric I was willing to "sacrifice" for my tester/muslin is a brown/ivory ivy-ish print that's been in my stash for years and years. While the pattern I created did actually work fine, I wasn't totally thrilled with the print crawling up me on this top once it was done. Until ...
... I whipped up a quick Magic Pencil skirt with the leftovers. Now I LOVE them together as a two-piece dress and will be wearing my new outfit to work this week for sure. I'm really liking the movement created in the different print directions meeting up, which itself is created by the odd-shaped front piece needed to create the top. Pattern morphing details/pics are below.
Here's a close-up of the gathered sleeve join on the left. The right is just a cut-on/dolman cap sleeve.
Here are the gathers going down the left front sideseam. (Which provides nice tummy cammo!)
From reading the reviews, the real pattern calls for a neckline facing of some sort, and nearly every reviewer had gaping/flipping trouble with it. If I hadn't read Lynn Rowe's excellent tips and photos from her review, here, I probably would've used a coverstitch binding around the neckline but I gave Lynn's method a try and it worked just great. (It's like a bias binding facing, except single-layer and cut with the stretch, not bias, going the length of the strip.)
So, I promised pics and tips on how I created my pattern ...
I started with my TNT Ottobre tee (of course!), which is just a basic scoop neck tee. Because I just had two successes in a row with the cut-on/dolman cap sleeve of Butterick xxxx (I'll fill this in later), I used it to create the shoulder/armhole changes to my TNT tee by just pinning the two together and then tracing. If you don't have a similar sleeve to trace, just look at the shape here ... I'm positive it would be extremely easy to create on the fly. It's a forgiving sleeve so you don't really need perfection.
To emphasize, I ONLY used the parts outlined in red below to "fill in" the armhole of my tee, so disregard the weird shape of that Butterick piece. It only needs to be weird like that for the Butterick top, not this Kwik Sew copy.
I laid a folded piece of pattern tracing paper over my pinned-together TNT and Butterick pieces and traced. I used the tracing paper on the fold so I could open it up into a full front piece after tracing/trimming. The full front is a must, as you'll see next.
Next, I used a combination of my curve ruler and eyeballing the photos on the reviews to create the asymmetrical neckline shape. If you look closely, you'll see a couple of "extra" lines where I drew a shape and then changed my mind. :-) The KS line drawing looks like it's just a straight diagonal line, but the pattern photos made me worry about bra strap peekage so I made my neckline more curved and did NOT make it wider than my trusted TNT neckline. (I'm happy with how it turned out. The bra does not show, or even try to show, at all.) After I committed to my neckline shape, I marked a couple of notches, and then sliced off the left upper, set it aside for the time being, and then added a seam allowance to the remaining neckline. I also used this moment to create a grain line parallel to the CF fold (you can't see it, but it's there) of the full pattern piece. Make another little grain line on the shoulder piece too. And if you're smarter than me, you'll do that before you cut it off. Not that I would know about that ...
Next comes the wacky part. :-) Draw a bunch of diagonal lines (6 for me) radiating from the right-side waist and going across the full front. Slice 'em apart, leaving a "hinge" at the radiation (?) point. Radiation? No, we're not nuking our pattern here. Hahaha. Ahem. Then spread each slice 2-3 inches each. Not rocket science ...just eyeball it so they all look fairly evenly spread apart.
Fill in the space with all that tissue you cut off from other patterns and save in a pile. Oh, you don't do that? Now's the time to start. You'll never have to use paid-for tracing paper to fill in alterations again. :-)
If you're OCD, this next part will make you nutty ... to create a new sideseam, just eyeball tru-ing all those slash/spreads so you end up with a smooth curve. Again, not rocket science. Not a fitted top. It's a knit tee. It should be smooth but it doesn't have to be perfect. If you look closely at the left side of the photo below, you should see a little piece of tissue I used to smooth out the sharp angle creating during the spread of the other side. I recommend you smooth out that waist area too if your pattern's waist curve gets too angular like mine did.
This is my back piece, which is really just my TNT back piece pinned to the Butterick back piece, since I knew the shoulder/armholes would match my front morph. I didn't even bother making a proper pattern piece yet since I was still testing. Now that I know it works, I will create a dedicated back piece before I unpin these.
One thing to note ... before you cut fabric, and really, before you do the crazy slash/spread to the front piece ... WALK YOUR SIDESEAMS. My TNT is intentionally ~1" longer in the front because the bust area is eased to the back piece. But this pic below shows an additional 1" discrepancy above that... which I didn't catch until I was actually SEWING the sideseams. Oops. Luckily, cutting off that extra inch didn't make my finished top too short. This is what can happen when pinning together two different patterns and thinking you're smarter than them. Yeah. Humble Pie time. In other words: measure twice, cut once.
Moving on to the shoulder piece. Basically the same radiating slashes as the front, but radiate from the center shoulder this time. Your goal is to keep the same length across the top/shoulder seam while adding 2" or so to the original slice/seam line. Doing this creates a *very* wonky pattern piece. I simply laid it out, before slashing, on another piece of pattern paper and traced it so I could return to the original shoulder line and neckline area (I also added a neckline SA to the tracing), and then I trued up everywhere else to create a smooth piece, curved at the bottom where it will be gathered to the full bodice piece. I hope this is clear. I know it's not a precise method, but the eyeballing thing is actually what I do. Remember, it's only a tee. And you're allowed to make mistakes. It's one of the best ways to learn.
Here are my final shoulder and front pieces, a little closer. Not sure this helps. :-)
To connect the shoulder and front and finish the neckline, go to Lynn Rowe's excellent tips and photos from her review, here. Then just evenly gather the left sideseam until it is the same length as the back (using your favorite gathering method) and sew together like any other tee. I simply turned under the sleeve hems and sewed with a slight ZZ. On my Buttericks with the same sleeves, I coverstitched them. Either method is fine.
I have no idea if my pattern looks anything like the actual Kwik Sew pattern, but my finished top does so I think it's a win.
If you have any questions, please ask and I will answer in the comments so it all stays together.