I think it is extremely unlikely that flight deck visits will be reintroduced. We now have a situation where all UK flight decks are to remain locked in flight, with access restricted to authorised F/As only. This has been agreed by the CAA with the airlines, and is likely to become EU and national law, as it is in the USA, and has been for some years.
If an individual captain agrees to allow aircrew from another airline on his flight deck, that is his prerogative - although he may well be acting against his airline's SOPs and the law!
Don't hold your breath, peeps.
PS Pre-arranged jumpseat rides, organised through the airline (including crew companions travelling on a staff ticket) are another matter, but even then it's a little awkward publicly admitting people in civilian dress onto the flight deck in view of other passengers.
[ 14 January 2002: Message edited by: Scroggs ]</p>