Any yes, HTML/JS/CSS can be used to build anything, but that's a bit like saying Assembly language can build any app: At some point you don't want to keep reinventing the wheel.
Of course, EVERY programming environment has tried this and it's nearly impossible to get something to work universally. I'm just asking for a very opinionated set of services and libraries on top of the web so it's really stupidly easy to build and SHARE things easily.
alcinnz