When the Brussels routes started, there was some horse trading with BMI mainline giving routes over to SN out of Heathrow, the payback was BMIr running some routes for SN out of the regions, so no real suprise that they have reverted back.
The 135 and 145 are not economic to operate on scheduled passenger services, thats why they are parked up around the world. Eastern are using them mostly for charter work, where all the seats are sold everytime, even if they are not occupied, and the aircraft are leased cheaply.
For any operation out of LHR a bigger aircraft is required. The competition (flybe) are running around with more efficient aircraft, and even they are struggling, so I cant see Bmir having any better luck with a patchy route network, innefficient fleet, legacy issues divorcing the company from its parent and a muddled business plan.