What to keep an eye on is noscript/basic (x)html interoperability, namely a web site, not a web app.

With a web site and not a web app, you are not dependent on the whatng cartel web engines, in other words, the door is kept opened for small and alternative _real life_ noscript/basic (x)html web engines/browsers (with CSS renderer or not).

Ofc, you can have a web app and a web site side by side, usually the web app is built upon the web site.

In the end, if we are all honnest with ourself, 99% of the time spent on an online service is keeping it available and safe, 1% will be its actual development.