As you go back in time, you will find that ZDoom is highly incompatible with itself. The reason Rex's Darkest Hour doesn't work from 1.22 to 1.23 is because ZDoom tended to change a lot of things without regards to how things worked and how modders were accustomed to previous versions. I'm sure the Odamex team would love to see full Boom and ZDoom 1.22/1.23 support, however there is not enough time in the day to keep up with demands and too few well documented bug reports to rely on. Its very rare that you come across developers that are willing to delve into the engine as thorough as some of the developers we have and we're lucky to have them. But the fact of the matter is is that there is nobody dedicated to simply "fixing compatibility." We would all love to see perfect DeHackEd, Boom, and ZDoom support (on and offline). But as of right now, development is a bit slow and the priority is netcode improvements, rendering improvements, and a more robust menu system simply because these criteria are what the developers enjoy working on the most.
If any developers are reading this topic and want to help the Odamex team out with anything coding-wise, please do not hesitate to contact the team via IRC or the bug tracker!