Well, if you're sticking with a K03 and internals, there's only so far you can take a 2.0T. Built or not, there's a limit on how much a K03 can flow. IIRC, my mechanic, an Audi/VW specialist said that with 1.8Ts, having a good tune once you go past 300 wheel horsepower becomes very important to avoid breaking the stock rods. I wouldn't be surprised if the 2.0Ts are similar.
Most of that applies to Mazdaspeed3s as well, though they start with the advantage of an extra 0.3L of displacement and a twin scroll K04, which (along with less weight) is why they'll definitely get into the 12s with similar mods, and high 11s on a good day with slicks. Not wanting to do internals is why I'm leaning towards a built K04 instead of something bigger. Even a stock-sized turbo can push the stock rods to their breaking point.
With modern engine management and design, turbo engines don't need to be as overbuilt as they were in the 1990s, which is good for OEMs worried about drivetrain cost/mass/fuel economy/etc. Still, I think a lot of the overbuilt reputation of 1990s Japanese turbo engines was overstated. They make aftermarket internals for all these engines for a reason.