433 mhz RF comms using external AVR MCU (advice on serial protocol needed)

Personally I'd just forget everything and do what's simple though. As long as it's easy for people to use it doesn't really matter if it's like any other protocol.

That's sounds similar as the whole (http/)HTML came to be... good principles to begin with, pragmatic easy to understand approach for each problem. Yes, it got us a bit into a mess - HTML 4.0 - HTML 4.1/XHTML 1.0, a dragging and finally failed XHTML 2.0. But HTML5 - like Phoenix out of the Ashes - kept it moving mightily. Yes, some is on the back of the Browsers which have to work even harder to keep accomodating all the legacy and do a good job on the new stuff...