Hi Simon,
I'm dealing actually with the same problem. Would you like to share your  "configure in my own subclass"?

I'm also thinking there is a need for a bbclass which actually is not using gyp, instead it should be able to "npm run build".

There is alsa a patch for speeding up npm npmsw fetcher https://www.mail-archive.com/openembedded-core@.../msg142406.html
cheers Thomas