I never really had a use for thief-acrobats
(they seemed kind of useless), so I don't remember, but it seems that they would be a sort of human-only class perhaps, if it requires a sort of special case of dual-classing (which only humans can do)... (Then again, half-elves were allowed to be bards in 1e (strangely), so...)
In my opinion, I think that having the ability to dual-class into a special class at higher levels would be best and quite useful (don't say "prestige class"
)... Besides the thief-acrobat, we have the bard, and also many Dragonlance classes like the various Solamnic knights (Order of the Sword, Order of the Rose) and the White Robes/Red Robes/Black Robes (Wizards of High Sorcery); there are even some Forgotten Realms classes (2e) that allow dual-classing for anyone (even demi-humans) (i.e. the various dukar classes of the undersea).
I would guess that dual-classing is probably hard-coded as a human thing for now in DC, but we could work with that, too...
(Just ignore demihuman dual-classing until the day when that becomes possible.)