HTML5 is actually pretty complete and reasonably stable. I haven’t heard a lot of issues with things not working. One thing that’s not ported in the Lua socket library, and this is by choice. It was bloating the app too much. There may be some native.* items that haven’t been made to work with HTML. Some things like native.newMapView() just doesn’t make sense for HTML5 for instance. You can easily call JavaScript to bring up a Google Map. Most plugins are designed from mobile SDK’s. They were never ported to Windows/macOS in the first place and it makes no sense to port them to HTML5.
For the last question that’s tricky. Right now Google and Apple are keeping our hand quite busy. We have to deal with Facebook soon and every changing ad plugins. I don’t believe we will be working on HTML5 in the near future, unless a really bad bug rears it’s head. Our interface with JavaScript is really good, so it’s really extendable.
Rob