Either EMB190/195 or CRJ-900X might be a goer - Air Canada have bought both for their long thin US and Canada routes and have reduced their 32x count somewhat. Pluses or minuses to both of course. Ever since WW there seems to be a big commitment to simplifying the fleet at EI and adding types might be seen as backsliding.
I'd like to see EI acquire a couple of more A321s so that LHR is always 321 once BFS is bedded in (given the price of the slots I would argue you gotta pack them in) with the ability to field some 321 flights on bucket/spade routes, not to mention that Gordon Brown is looking at moving to a air tax regime which might favour larger aircraft on fewer frequencies.