How about making that new AFV model the AFV mark II so there's an actual point to making one when the comm researched upgraded chassis but not HE or Ranged. Light Tank mark II could do with something special as well.
I think that just making mk2 replace mk1 instead of having a separate chassis for both would be better. The extra slot would just be an improvement, not a separate chassis.
Just look to the Art forum. Some peoples are already making new models. http://forums.empiresmod.com/showthread.php?t=8707 http://forums.empiresmod.com/showthread.php?t=8580 http://forums.empiresmod.com/showthread.php?t=8568 http://forums.empiresmod.com/showthread.php?t=9187