The factions that I would like in EB if we didn't have _any_ limits:
Goidils, Caledonians, Belgae, all German tribes as one-province factions, Lugiae, West Balts, East Balts, Proto-Sami, Neuri, Scythians, Noricum, Helvetii, Lusitanians, Celtiberians, Southern Iberians, Scythia Minor, all greek colonies on the Pontus coast as one-province factions, Tylis...
and that's just for Europe :)