Old websites still run very well.

Is there any reason to believe that a major new browser tech, WASM, will ever have support dropped for its early versions?

Even if the old versions are not as loved (i.e.: engine optimized for it and immediately ready to be executed) as the old versions, emulation methods work wonders and could easily be downloaded on-demand by browsers needing to run "old WASM".

I'm quite optimistic for the forwards-compatibility proposed here.