[pharke]

It would certainly be a challenge but there are examples of cross platform applications that have succeeded in the market. The Godot game engine is a good one since it does a similar thing for a different segment of the market. It's cross platform and allows you to build applications that target those platforms and more (even the web!). So these things are within the reach of a small team, or even a single dedicated individual. The important thing is to focus on what matters. Providing a safe environment to run code downloaded from strangers, a set of configurable UI elements and an API for making network and storage requests. You're basically building a VM with a UI kit and some networking. You could probably bootstrap up from something simple since it would likely be a fun platform to target for hobbyists, if you could build a community or scene around it.