I haven't read all the posts, just tried to get a general gist, so I'll apologise in advance if I'm slightly off topic or missed the point, i don't really use forums that much.
I don't know about you but there are a lot of firearm certificates out there to me. 151,413 firearm certificates on issue at the end of March 2014
-link-
Personally I think if they did regulate paintball markers, it would be closer to the shotgun licencing of which there were 582,923 shotgun certificates on issue at the end of March 2014.
I know a few shotgun licence holders and I basically treat my paintball Marker in a similar manor, I.E. only carry it on me or in car with a purpose (going paintballing / cleaning etc), I'm personally reluctant to fire it in my back garden.
I wouldn't have a big problem with them licencing it as it appears to be in some locations, and then at least it is defined.
I am a member of a few re-enactment group's (Roman, Medieval, mainly) so I also own various swords, spears etc. these aren't licensed either but as I think Dusty put it, just don't go waving it about and it should be all good.
I am assuming in places that it is licensed it's not particularly difficult to get a licence?