Nev, at the moment excess crew are burning all their leave so that liability won't exist in a couple of years time. Every mainline Captain is on 12 year pay so getting rid of senior 744 captains by paying excess VR doesn't really achieve anything. The captains that go to the 787 will still be on 12 year pay- which would be identical to what those 744 captains demoting to the 787 will be on. Whether they can afford the pay cut from a smaller aeroplane and less overtime with the 787 likely to do some domestic flying as part of it's makeup is another question entirely.
The ONLY reason to offer VR to senior Captains is to avoid multiple training courses that demotion may throw up. Even then, if a 744 Captain displaces someone junior to them on another fleet it's about seven training courses. I'm not sure what the cost of that would be but would find it hard to believe it'd equate to 2-3 times the 'normal' redundancy pay out. Besides, given that redundancy is normally last on, first off and 6 months pay, they're going to need to offer decent packages to get any one else to take it. See my previous point about the 'cost' of retraining courses compared to the VR they're likely to offer as to whether it's worthwhile.