This is a bit of a reach unfortunately. UTF-16 (most often broken WTF-16) is still the standard text encoding on NT. The manifest change only makes A-suffixed functions always do a "UTF-8 to UTF-16" conversion, instead of the unhelpful "local codepage to UTF-16" conversion. Sure, that's better, but:
- Microsoft has expressed no interest in switching the actual underlying encoding to UTF-8, they will likely never do so in NT.
- A-suffixed functions only exist for some Win32 API. Newer Win32 functions are defined only taking Unicode strings. All COM, WinRT and native (Rtl/Nt) APIs use Unicode strings as well. The UTF-8 API surface is actually quite small - one might have to step out of the UTF-8 comfort zone in practice.
- Performance is being left on the table. Transcoding still has to be done, it would be more beneficial to at least keep it local for optimization purposes. The most trivial, yet still important use case: constant string conversions can't be optimized across DLL boundaries.
- Unlike, say, DPI awareness mode, there is no official API to change this behavior at runtime. It has to be done through the manifest, a compiler implicitly embedding such a manifest into every executable it produces is not ideal.
TL;DR: It's an improvement, but just barely, so bumping the minimum version just for this "feature" is not worth it IMO. Just bite the bullet and convert to UTF-16 if you have to, it's conceptually simpler and likely faster, too.