Pace
My apologies, I should have made it clear I was talking VFR. I agree with what you say with one slight caveat. The CAA plan includes what it called phase 3 of the process. This was ADSB using ES on mode S. The most popular mode s transponder in the UK by far is the Garmin GTX 328, which is also the only one which does not support ES so cannot be used for ADSB. There is a very real risk that people who have fitted the GTX 328 (at a typical cost inc installation of £2500 ish) will have to throw it away and replace it!
One other issue is cost. It is now possible to get a mode s unit for about £1250 inc vat (with ES). Seven years ago when I was designing and building my panel I was quoted £4500. I got a second hand mode a/c as a stopgap, which is still working fine and has saved me a lot of cash. There is at least one company who are developing a transponder, which can be remote controlled from an EFIS, so is not panel mounted and has no user interface. Target price for that last time I looked was £600.
Add up the cost saving and the regulatory situation and it can be a good idea to wait and see. I have been in this mode for 4 years and expect to stay in it until at least March 2012.
Rod1