The OV-10s biggest problem is that it's not a jet...and many people cannot get past that fact, much the same as the A10 has always suffered because it can't go supersonic
A relatively low speed shouldn't really be an issue. After all, the Apaches are hardly what you might call fast air, but you don't hear anyone complaining that they are too slow. Getting ordnance onto a target area should be the priority, probably with persistence to cover troops and a relatively high degree of accuracy to deal with danger close scenarios. Whilst a supersonic ac would bring lots of noise - good for shows of force - and the ability to get to a TiC quickly, both of which are v useful characteristics, they are about the only pluses over something like the Bronco.
As no defensive aids that I know of will fend off RPG's & AAA
Without delving too much into this here, a well flown platform adhering to the correct tactics and with a bit of luck thrown in should be fine against unguided systems. The development of hostile fire indicatoris for use against these sorts of systems should also be a help, and would hopefully be an automatic fit for any slow / low platform operating in this role.
All in all, I think there is a quite sizeable market for a Bronco or similar platform.