Dear Ivo, just some personal thought about the" elusive" Joomla 4 : the release for beta version, at first announced for October 19 and then for March 20, has now moved to May 20...and that's only a beta, not even an RC!!
I love Joomla, I've used it for all my websites starting with 1.5 version and upgrading through the years, but now I feel the team is at least "unfair" to all the Joomla users and developers.
Personally I'm now trying a test website built with GRAV, Gantry 5 and the free "Helium" theme by Rockettheme. Well, I'm amazed at how fast this site is ( A in Google Page speed with an amazing 92% score and 1.7 sec, uploading time). I used some of your GRAV specific particles (News Pro, Slideshow) plus general ones like Portfolio and Contatcs. They work like a charm, seamlessly integrating in Gantry 5 + GRAV, with only minor customisation of scss.
So my question (and my hope, too!) is that IT may in future work on a new "branch", developing particles and templates for GRAV- I suppose that it's worthwhile, since the web is all about speed and high performance and this will be more than true in future too.
Be reassured: this is not a critic to your astonishing work, (you have all my support, as usual) but a source of inspiration for new development of Inspire Theme