In reply to mark k..

As I said it is a bad confusing practice to have non uniform code. If core rest API can be written in 5.2 syntax I can't see why BP can't.

so REST API for core is something that you have to do with 5.2 syntax but the same code moved to BP will need to be changed to 5.3 (and it is worse going the other direction)? and even in BP similar code will be written in different ways. This is just bad software engeeniring.

+1 for dropping 5.2 to reduce support effort, but that is all it should have been about.