Well, first of all I don't think you need to worry about any other BI mods coming out in the near future. It's your mod and Attila's, but "Fall of Rome" and "Imperia Romana" is both struggling with loss of manpower and might be dying away ( even if they never will admit it, of course ).
Yes, the two turn thing for "native Romans" might be a good idea.
And another thing: why can't the ERE bribe the WRE armies and vice versa? I mean, when playing as the WRE or the ERE, it is not possible to bribe the other Roman factions, why is that?