I'm sure there'll be lots of rule-bending but those of us hoping to get £50 of free upgrades on our existing bikes are out of luck.
Depends how well you know your LBS and what deal you can strike with them.
I'd discussed buying a "bike" from my old LBS through the Cycle2Work scheme that looked nothing like a bike. Turned out it wasn't worth it and I'd have probably wimped out of doing it anyway (I prefer rules).
It was just a bunch of expensive components (e.g. PowerTap hub built into custom wheel, plus some other bits for other bikes) that came to ~£800 or so. The voucher was going to be for £1000 with the LBS not seeing £100 of that as it goes to the scheme administrators. The other £100 was to cover the much lower margin on the bits I was ordering compared to what the LBS would have made if I'd ordered a £1000 bike.
Once I'd worked out I'd only get £800 of bits for a £1000 voucher the savings through tax were all but gone. The only benefit would have been spreading the payments out over the year through salary sacrifice and that can be replaced by 0% finance most places are offering.
I would have expected an LBS wanting to do a deal that would offer you £25 or £30 off components in exchange for the £50 voucher for doing no actual work on your bike. It depends on what the LBS gets back from the voucher.
Anyway, all relatively moot for me as I don't need this service as I can fix my own bikes, plus the vouchers will be in limited supply so I'd rather they went to people that really needed them rather than people who don't.