TL;DW: there is interest in supporting Typst, but there are roadblocks:

* Higher priority work currently being done on ArXiV (moving from Perl to Python/cloud)

* No "standard" Typst distro

* Support team needs to be re-trained for a new language

* Persistency: TeX has 30+ years of history; will Typst be around in 30 years? Will current code compile? Will existing documents be supported?