As the Ferengi of the Star Trek series might say, “Where is the profit in that?” FreePBX and its open source version likely make little money for Sangoma. I suspect Asterisk will continue but I’m not optimistic that FreePBX distro or PBXAct will move forward. Look at all the layoffs and resignations from these teams.
Perhaps, someone enterprising like VitalPBX or a newcomer will release a more open-source GUI that actually continues to move forward with Asterisk. The other alternative will be that Asterisk 21 will still allow macros and chan_sip. That would be the path of least resistance but I seriously doubt the FreePBX team will have the manpower or budget to actually modernize their product to update badly deprecated subtending requirements.
If it comes down to nothing but community support for FreePBX, maybe its time to dust of the old open source Asterisk GUI and bring it up to speed with Asterisk and current security practices.