Wordpress with a cleaner architecture and a more modern API wouldn't be a bad thing.

Maybe give the WP REST API a spin.

Very active development, but needs more real world examples before its ready for WP core.

http://wp-api.org/

Well... no thanks. :)

Wordpress has some undeniable qualities for quicly building simple websites. Making it a whole framework for apps and big websites just sounds silly to me.

If I need to build large webapps I don't see any reason to do it with Wordpress (or even PHP) nowadays.