I just watched ssolie's AmiWest 2022 talk on ExecSG, where he also mentions the need for a firmware update for the X5000 (and others) in order to make use of OS4 with multicore-enabled ExecSG currently under development. Summary as follows:

"Solie is also responsible for firmware updates. The U-Boot versions for X5000 and A1222 plus not only received various bug fixes, but will now also correctly initialize the additional cores of the multi-core CPUs used in these machines. Firmware updates will be distributed "soon" via A-EON. Once they're installed, the respective computers will then be "multi-core ready"."
http://www.amiga-news.de/en/news/AN-2022-10-00104-EN.html

Does the opening posting of this thread still apply, now that it's 2 years later?