There are two sets here, and Britonnians appear to be the most consistant and repeating army that I could dig up. So lets look at these possibilities, and will continue to dig for something much more solid. Please remember that these are rumors, and to be honest, you need to apply lots of salt. My rumor sources and lines to get Warhammer Fantasy information are fewer than my 40k ones.
Bretonnians/Wood Elves (I think the wood elves are wish listing)
This would place the first one sometime in Q1 of next year. Other rumors place it like this (although I think the above is much more accurate. Either way, I would say that Britonnians are next.
Bretonnians ------ March
High Elves ------ July