Studi,
I have no idea where you are coming from but lets look at both your scenarios.
1. BMI will slowly be dead, pilots transferred to BA, slots taken over for longhaul expansion at BA. The whole BA Express thing was a bluff. So no need in the beginning for pp34 etc.
BMI won't be slowly dead, either it remains as an AOC holder and a seperate company within LHR or it gets merged into BA. BA does not have enough long haul aircraft to transfer the slots to. There is not enough manufacturing capacity to make enough long haul aircraft to fit the slots in the short term. Not only that for Long Haul slots to be 'valid' you must tie them together with arrival slots at the destination and routing through the global NATS structure. Neither of which come cheap or easy. If that were the case then I'm sure Lufthansa would have done it.
If BMI is to be pulled into BA it will have to continue to operate its slots within the structure of BA Short Haul as the BA scope clause states that any aircraft operated out of LHR which is owned and operated by BA must be flown by mainline pilots.
Thus the lists, legally, must be merged. IAG want payment for this option.
They don't want more pilots working to 65 on 24 pay point scales.
2. BMI will be used as a vehicle to take over planes from BA. So now of course BMI will be profitable. Now the pilots have a case to fight for better T&C.
Why isn't BA shorthaul profitable out of LHR? If it is so easy for BA to make BMI profitable why haven't they done it in their own back yard so to speak? I don't know if you operate out of Heathrow but, in the simplest of terms, the turnaround times other carriers enjoy in smaller airfields are impossible to match. The hours flown per annum by LHR SH pilots is lower purely because it can take hours to turn the aircraft around at London thus eating up your available FDP. Oddly enough this also precludes your other premise of a 'Lo Cost' model for Short Haul BA. It would not work through Heathrow.
Now look at the 'profitable' BMI, they threaten strike and the 'non expansion' BA crews are there to pick up the routes. Catch 22, BA SH Mainline have seen their aircraft disappear, their routes disappear and their future prospects disappear into an airline which is now striking for comparible terms and conditions. Long term strategy you say, long term suicide is the reality.
The only problem with trying to use IA to push up your T's & C's is that you need to make yourselves indispensable, if you're not then the wet leasers, opportunistic flight crew and ruthless management will lunch you.
The logisitics behind running a SH airline and a LH airline are very different. Combining the two is also very tricky.
I don't seem to remember any major successes on T's & C's from Vereingung Cockpit outside of the outsourcing of the pension funds.