The latest certified JBoss is AS5 which is EE5 certified.
AS7.1 will be full certified after release which will comming soon.
To use a not certified version is on your decision.
I saw often installations using not certified servers (e.g. parts of EE5 in AS4) also applications breaking the spec.
But if you test your application well and it works for you ... why not?
If you use ony EE5 features and be (mostly) conform to the spec and using EE standards you might use AS5.1 and move to AS7 later.
But AS7 will be smarter, faster and for sure cool stuff I won't miss . You have to learn about the new configuration and app packaging because there is something different but on the other hand you will be up-to-date.