TBH its just a few days until we can find out for certain π
My thoughts...
A $100 plug and play device will not be a perfect thing, expectations need to be kept realistic...
Since all 5200 games have A8 ports I'm not sure there is an issue with real 5200 games - and yes I know some actual 5200 games use proper analogue controls - I doubt The400 will support that...
The carousel will not be editable based on the previous hardware (A500), but I have found that is largely irrelevant since you can just load anything off USB - I have all their other machines and whilst I dabbled with the carousel alternatives on the C64Maxi (and it was a fun time sink), I went back to stock and found loading off a well organised USB stick is much easier...
I have found that some 3rd part controllers work, lots do not - the supplied one(s) with their other devices have been pretty solid IMHO, so not really a worry...
sTeVE