I can see bolting a fallback regex mode for the few languages that have features which ts cannot (yet) accommodate.
And 'niche layered on niche' is -- well, it leaves me wondering how much you've actually used hx. The experience is nominal, the installation is sane, and it was way faster to get to 'genuinely pleasant' than nvim ever was.
As a plus, nix home-manager also handles helix config, which, as a nixos user, puts it over the top for me.
(home-manager also does nvim, but this is mostly mooted by my need for an elaborate (and turing-complete) Packer configuration, which has me using a separate git repo for nvim specifically)