While MENUdo may only have ROM loading for one flashcard in the end (IF Soul sells out), it'll still be able to be run on all flashcards, just no ROM loading. Homebrew works fine too, and all the other features will give you plenty to do.
As for who has what flashcard, like Placeholder said, Soul's set us up with a special version of MENUdo that runs ROMs on most flashcards for the time being. I'll come out with it - I own an M3 Real and an AceKard2.1. Used to have a DSTT, but I sold that to my friend. But either way, ROM loading with MENUdo now may be totally different from ROM loading come release time. We can't say yet which card(s) will support ROM loading on release day.