From the top of my head, it would be nice to have Jakarta Config in EE 11 and some other specifications using it for configuration. In general, pulling some features from Microprofile that fit Jakarta EE would be useful, e.g. Rest client, which nicely fits into Jakarta REST already.
This is certainly one of the major themes to consider as well; moving features from MicroProfile.
MP JWT makes a lot of sense as an additional authentication mechanism for Jakarta Security. In practice, a variety of implementations already use it that way. It would be interesting how we would exactly do this. Copy over the spec text into Jakarta EE? Reference a specific version? E.g. Security 3.1 saying under "provided authentication mechanisms" something like:
"Support for the JWT authentication mechanism is required, as specified by the Microprofile JWT spec, with the following additions/changes..."