ALLMCC->Looking at the numbers using it would suggest (assuming respectable yields) that in summer it could sustain 3/4 times a week in an ATR 42 in summer. I'm not sure when Aer Arann go to an all ATR 72 fleet, but I think they should still have 42s next year.
Winter might be a different issue, but I would imagine Belfast-Galway could probably be made to work year-round by an airline with a bit of patience. Both are sizable enough population centres and non-air transport links between the two rely on using a private car on poor roads.