bookworm
3) Not to the best of my knowledge. I would say its buried in one of NATS (in confidence) papers somewhere. I have access to several NAS experts and asked them.
4) The original plan was in the long term NATS strategic business plan and was due to be complete in 10 years time. This plan is now on hold. No deduction on my part. No, these details are not published in the public domain. If you're a NATS employee mail me and I will point you to the plan on the intranet, its not a secret.
Sorry if I seem to be only telling 'bits' but obviously company confidentiality forbids indiscretion.
Part answer to 6) for UK is that because NAS FLAT tracks aircraft the UK does have the ability to use specific codes for more than one aircraft. So it is quite possible to have several aircraft on the same (preferably one of the sector discreet codes) code, but with the TDB displaying the correct callsign etc. But we do not do that.