FWIW, the fonts issue isn’t a technical limitation, it’s a legal/licensing one. Font foundries license by the seat, and scenarios like docs where documents can be shared outside an organization and the font travels with it are against the rules. Office online has the same issue for the same reasons.

There are exceptions, where a company has developed a font internally and owns the font directly, but those are far and few between. Even when a company has commissioned a font from a foundry, they’re usually licensing it from the foundry rather than owning it themselves as a work for hire.

(Source: googler, used to work on workspace, and through a random series of events ended up working closely with the google fonts team on this problem)

EDIT: also, you should be able to use apps script to do document generation from templates, that’s a pretty common use case.