I understand what you mean, and if fact faster payments will be the route through which bacs will be modernised - if you look on BACS's website today, you will see that they are celebrating their 40th anniversary! A new system is long overdue, considering the evolution of technology over that time - I'm sure that 40 years ago it was not imagined that we could talk like this!
You are correct in saying that the OFT have been investigating the BACS process, but this is only to ensure that banks are adhering to the 3 / 4 working day timescale, which is an industry-standard.
Without widespread acceptance of the faster payment system, CHAPS is an alternative, and most banks tend to provide this service subject to the payment of an administrative fee. The timescales are generally same or next business day. CHAPS should continue to exist after complete adoption of Faster Payments since APACS and the participating banks will impose transaction limits on faster payment transactions - currently these are £10000 for individual transfers and £100000 for standing order payments, but banks will be allowed to set lower limits. This may be to limit the possibility of fraud through the system - CHAPS generally requires extra security, such as presenting ID at a branch or written requests.
It should be noted that faster payment may not be extended to all accounts, particularly savings account which do not have a sort-code - often building societies and former building societies have such accounts which are identified by a roll-number. Faster payments will take some time to be fully implemented because of the complexity of the change - it is vital that the change is delayed until individual banks' systems are ready. Having personal experience in CHAPS, it can be very difficult to resolve problems when payments go awry between 2 banks.
Banks aren't required to offer the service, however they will find it is commercially advantageous to do so. If you don't want to pay for CHAPs and bacs takes too long, then you could withdraw cash from one bank and pay it in at another, but I certainly wouldn't be spending my Saturday mornings doing this. With Car Parking charges as they are, I think I'll accept the lost interest!
Hope this helps,