There is a standard write-once-run-everywhere platform. It's called the World Wide Web. Browsers have turned into very advanced VMs with access to native resources that Java could only have dreamed of. There is even a bytecode IR called WebAssembly. I want to see all HTML5 APIs exposed to WASM directly without the need for JS trampolines. It would be nice to be able to target web browsers with any compiled language.
2) As a next step, it is necessary to implement access to more hardware. Why shouldn't a web app be able to talk to arbitrary devices if you grant it access to that? Suppose I want to use a web IDE for embedded development and I want it to talk to a JTAG programmer? Suppose I want to use a software synthesizer and I want it to talk to a MIDI keyboard and an external audio interface (in low latency synced multi-channel mode)? That kind of advanced stuff still isn't possible.