FullyFullyReady
I wouldn't recommend commuting during your intro to BA. (Though I suppose you could?) So that would cover about the first 6-8 weeks. (Cheapish accommodation available) After that I can't see why you couldn't commute. It could work just as well for you as anyone senior. Though I think it's 6 months before you qualify for staff travel?? Also you might expect to do more standby duties than seniors, which run for 4 weeks, including 7 'fixed' days off, plus other 'ad hoc' days off during the 'working' 3 weeks, including a 2 day block. (Perhaps one Reserve month per year????)
alpha.charlie
In BA there is an Engagement Freeze of 5 years. Because this is based on qualifying training years, it is often less. During this period BA will do with you whatever suits them. Including for example, changing your fleet of joining!!
Since freezes are only type freezes, (not base freezes) I can't imagine any circumstance where you couldn't transfer to Heathrow Airbus after an absolute maximum of 5 years.
Of course by that time you will also have a valid bid to other BA fleets too. Success based on availability of course, but Airbus transfer LGW to LHR would involve NO additional freeze. It's essentially a freebee!