I hear the Smartthings API is completely different starting sometime next year. Does that mean WebCORE on Smartthings is end of life, or is it being ported onto the new platform?
The new API already exists and is continually developing. It is the legacy services which will be turned off and webCoRE uses legacy SmartApps. So yes, its days are numbered on SmartThings in its current form.
ST are intent on developing their Rules API to the degree where it has most of the functionality of webCoRE (so not the stuff it does by bypassing the ST API) and the proposal was that webCoRE be rewritten to become a front end. However that proposal was about fourteen months ago and no more seems to have been heard of it, or at least I haven’t heard.