Re T3's likely replacement aircraft, you guys can speculate all you like as to capacity requirements but you are glossing over the main issue.
T3 are not (crrently) a LoCo airline, indeed their fares are on many occasions extremely expensive. I was a reqular commuter on the NCL - BHX route last year and the J41 was NEVER full. The early morning flight tended to be the most patronised with c. 20 pax. but "off peak" flights tended to have sub 10 pax. They made their money by charging c.£180 for the round trip, you booked electronically and similar to EasyJet the price varied according to the usual parameters but was never advertised at less than £134 though I could never get that rate. I did see the rate as high as £296 on occasions.
So you get the point, you will never fill a 328 or any other similar capacity aircraft with this pricing structure. Changing this strategy could become very risky, though maybe it may be forced upon them i.e. you can proably fly NCL to BRS return for £50 and get a taxi to Birmingham cheaper.
So I can't see a significant number of larger capacity aircraft being acquired in the medium term.