But then you don't have a nice REST API to integrate with different things anymore (authoring tools. exporting tools. frontends for devices that don't like meteor. ...)
IMHO tying itself to a single front-end technology would be the totally wrong thing to do.
Meteor is not tied to any single front end technology, nor is it a front end technology. It has an optional templating system, but lots of people are using react now instead. I love meteor, but using meteor with wordpress sounds like a nightmare. I think it was probably suggested more as an alternative.
Ok, then I got that wrong. Meteor apps always seemed incredibly coupled and integrated to me, so I assumed it was one "package".