sooo, the latest Lucky Bancho Lodestone census is out, this time including some numbers for Eureka. According to those, the number of active players per region that have started Eureka is:
58,8% JP
41,4% NA
44,2% EU

and the number of active players that have reached the Pyros level cap of 50 is:
18,6% JP
5,8% NA
7,3% EU

I'd say those numbers speak for themselves about how 'popular' Eureka is