I think Bellator's only got two notable problems. The first is that even though it didn't happen last season, there is the possibility that one of the winning fighters might suffer injuries from their fight and have to pull out. Not sure what they would do in that case. Second, they don't have champions in all their weightclasses. The three other weightclasses that don't have them are bantemweight, lightheavyweight, and heavyweight.
And the WEC doesn't have WW, MW, LHW or HW
I Think Bellator is fine running from FW to MW