The advice about grabbing an upgrade has always been good. It still is.
However, when TFly first kicked off, there were substanstial disincentives for BY guys to go across - lower salaries, basing, type freezes and lower pension terms to name but a few. Also, at the time, there was little if any hint that the two operations would ever cross pollinate to anything like the degree we have today, the implication being that the 756 fleet would not contract, commands would be available and so on. Times changed; the 756 is now seen as a shrinking fleet, the 73 is running some IT routes and there is an more open basing policy. The guys who went across in the early days took a big punt and I'm delighted it worked for them. They risked much personally.
As has been said, BALPA then negotiated equal T & Cs, the basing policy opened up and much of the risk went so it was suddenly a good place to be for gaining a Command or getting into training etc. The DEC uptake was a stop gap and it doesn't seem to have worked so well for some of the DECs. They have my sympathy but something has to act as a filter for all the varied groups, all with their own interests. Seniority is it.
There are several separate issues here that only touch loosely: Seniority, seat, base and type. The only unifying factor is the bid.
The company will (and has the perfect right to) put aircraft wherever they want. The same applies to their decision to do MFF (which BTW is now fully approved) and to do it where they want. If that doesn't suit you then you must resort to changing your bid. That will be looked at based on seniority (and ability if seat changes / training positions form part of it). I'm sorry if that upsets people but that is the way of the world.
It is pointless saying "I'm a senior Captain based in MAN and I want to do MFF and what makes it worse is a junior guy doing it in LTN". MFF is not running in MAN so I'd best bid for LTN and do it now because I can't displace a junior guy once they actually fill that slot. Stop me if I'm wrong but I personally have never seen a gun being held to anyone's head at either contract signing time or at bid time. You can change your bid any time, that's why it's called a standing bid. There are only root and branch bid runs when there are fundamental changes to the operation.
And finally, my understanding is that MFF will run at LTN first as a controlled experiment - a small base that needs MFF to satisfy the operational requirements of the company. It will then roll out further afield but probably not to MAN and LGW because the operation is big enough to support two fleets of pilots. The added wrinkle is that it will be 737 NG (most if not all Classics will soon be gone) and 757 summer, 767 winter. Why ? Because that is what the operation demands. There will be issues with forced base changes as we already know for sure but that is to do with airframe reductions at thiose bases and not as a function of MFF.
The eternal advice stands: Bid for what you want in terms of seat, base, type and type of operation rather than what you think you will get. If you don't get what you want it is because you a) didn't bid (numpty) or b) are junior to all the other people who did get it (live with it and your time will come). Seniority is global.
The one thing we absolutely must do is avoid the petty internicine warfare bewtween the perceived haves and the perceived have nots. When the company does all this they will be facing costs they will seek to avoid. Some of those costs will be those due to pilots forced to move and that is covered by BALPA agreements (subsidised by some here - enjoyed by all). When the company seeks to avoid those costs, and they will, being a fragmented bunch of self interested groups will hand a strong bargaining chip. Ever heard of divide and rule. The company has.