I think some publicity wouldn't be amiss on the MAN-SOU. The 3 x daily Flybe Dash 8s had good loads.
Domestic travel is increasing & the train from Manchester to Southhampton is the best part of 4 hours & first class fares are eye watering.
I've made a few train trips and they are pretty full.
The Eastern fares are almost half the Cross Country First fares & I'm sure people would prefer 45 minutes in a tube as opposed to 4 hours on train.
Trouble is in my area very few people are aware of Eastern, it's not really a know name in the Manchester area. However, it does need to be double daily ( which it is, only 2 days week)