From the department of not entirely formed ideas :D
Recording a podcast with Neil y'day, we were discussing certain modern, or less so, rule mechanics, in which I referred to one of the more modern trends (a ruleset with dice based activation, in fact) as a 'fifth generation wargame'. I was rather pulling the number out of a hat, but on reflection it's there or thereabouts...
1st generation is Wise/Grant/Featherstone
2nd generation is WRG and similar systems based on a big CRT
3rd is WAB/WHF/40K buckets of dice systems
4th is where IGO/UGO stops being the norm (card based etc)
5th is more advanced implementations of 4th - there is definitely a line here - IABSM is 4th, CoC 5th, IMO.