I always thought it was bizarre that there's no serious selfhostable FOSS virtual tabletop software [1]. The overlap between the two communities is very large and passionate. Foundry is selfhostable but it's a clunky proprietary node.js application and there's a ton of janky UI issues. Roll20 is far worse. I presume that this Diceright project is better since it's actually using a canvas. But why doesn't someone just use a proper game engine that can target the web (with wasm/emscripten/etc)? You're making a game after all, and it would mean that people who are happy downloading and running a native application locally for better UX would be able to.
[1] edit: That I was aware of when writing this comment initially.
Edit2: For an example of why gamedev toolkits don't necessarily produce performant, highly usable software, check out Dungeondraft (https://dungeondraft.net/). It's built with Godot and gets the job done, but as an application it's a total mess. I'm working on an alternative but (surprise!) it's a challenge.
Criticism for Foundry aside, it's an extordinary effort to implement a mature self-hosted alternative, especially as FOSS implies it's going to be a side project for most if not all of its developers.
Foundry's upside is that it's extensible (modules), which increases traction and nurtures a community.
Most of the FOSS attempts will probably die if they won't take that approach (extensibility that is).
Yeah that's how I see how it would work. Just build a framework for the players to interact in according to the basic mechanics of tabletop games and then expose a rich module API and hand it off to users. If you're clever about it I could imagine you could machine-translate the art asset formats made for Foundry, or design it to use it directly.
People who are into D&D and people who are into open source programming already both have time consuming, creative, indoor and sedentary hobbies. I think they mostly look for additional hobbies that scratch less-overlapping itches.
[1] edit: That I was aware of when writing this comment initially.