The problem with targeting a subset is there's a ratchet effect with web APIs, once support reaches critical mass in the major browsers sites will start unconditionally relying on those features and there's no going back from there, any new browser has to also support those features or be considered broken.
I suppose anything that's gated behind a permission prompt in Chrome/Firefox/Safari could be culled without too much trouble at least.
I suppose anything that's gated behind a permission prompt in Chrome/Firefox/Safari could be culled without too much trouble at least.