@DavidCarlisle Oh, very advanced. I now did a grep in the font files, and it seems to be only cambria and stixtwo. Cambria has useless wide hats, checks and tilde, and stixtwo has ibreve, iogonek, dottlessi, and a few more. Seems like something one can live without.
@mickep in lmtx math can you have a variable alphabet (like class 7) without giving up the mathclass for spacing. Could you have a variable font \mathpunct "?" ?