Maybe this feature could be added by using the relevant LyX code?
It seems that Lyx has lost its dynamism. They have not released any new versions for almost two years. Whereas they used to come out almost every couple of months.
I’m not sure supporting Lyx files could make TeXmacs more popular. But some Lyx features could be adapted to TeXmacs (for example list environment management, see discussion here).
Excellent latex import and export (generally speaking it’s already very good in, but the beamer class support is not as good for example) should make TeXmacs more in front of the scene.
Another feature that could make TeXmacs more popular is the variety of formats supported when exporting. I have pandoc in mind (look for example what quarto as achieved in this domain It’s pretty impressive).
There are already some works in this direction, see for example the markdown converter plugin.
Maybe the Mogan development could go deeper in this direction ?