For me the Maquis were the most interesting group in all of ModernTrek, by far.
A surviving splinter group of Maquis headed by her would have made a far more interesting 'nemesis' than miniPicard, especially if it turned out they weren't working entirely at cross purposes.
If you wanted a better INS, then when it came to asking hard ethical questions, it'd be better to do it with Ro on the other side of the table than the Admiral of the week and the Facelift of the week.
And Forbes is sufficiently outasight as an actress that you wouldn't need to do much backstory explanation, because you could sell her convictions based on an expression.
Hadn't ever thought about this till now, but yeah, Ro absolutely could have made a huge dif in the TNG films. The character alone brings a conviction that the TNG films pretty much lack (except maybe Soran in GEN, where it doesn't matter because it is hopeless, and in FC, where Picard's convictions are overstated, overplayed and downright embarrassing.)
Yeah, the bit about needing to believe in something from SERENTIY sort of shows what TNG films only pay lip service to, because even when there is blood spilled, the pain in the drama doesn't seem to really hurt. Then again, I think Whedon would have fled in horror at having to deal with the TNG characters, except maybe Riker on a very good day. His take on things seems much more TOS (as in REAL) Trek.