What do you mean? It will likely be backward compatible with BT 4.2, possibly even firmware upgradable to BT 5, current Macs will only be able to connect at 4.2, new Macs will likely be able to connect using the W1 chip and BT 5 as well. I'm sure the W1 will ensure AAC encoding throughout, but otherwise, it'll be standard BT.
I mean are we limited to SBC (required) and AAC (super likely). Are they going to throw in Apt-X or some new codec hidden in iOS 10.