You could do it in such a way that older bot's could be considered to have more module space as they have less specialised features than say Dashbots, Hovers or even newr bots like the Hellburner or Mercury - older bots with NO special abilities (that is, can't jump, can't shield, etc) could have 3 moduled, old robots which do have a special ability (Brit bots, the Griffin, Rotaga, etc) could have 2 module slots and the newst bots plus Dashbots which have amazing abilities maybe have 1 module... maybe even no modules as they are so specialised.

You should give older Robots more module slots than newer bots.