Wasm is build as an efficient target for C/C++ like languages. It's mostly a striped down portable CPU intruction set. Graal/Truffle is intended to be an efficient target for everything. It's a toolbox of crazy magic for building your own JIT.
There are not equivalent.
What if somebody will build a GraalVM-based browser? That would be something. Anyway, W3C recommends WebAssembly but does not impose it. It is not too late in the game because WASM doesn't even have DOM access, yet. And also people are still using browsers that are not WASM-ready. How many people actually compile their libraries to WASM today? Aside to early adopters scattered around Rust and Emscripten.
I don't see which actor in the industry (outside of browser makers) has the human resources to make such an experiment.
Mozilla were the one lobbying for wasm... and chromium has abandoned pnacl because of them. The only hope might be microsoft.
Oracle could do it in theory but I don't expect them to do it anytime soon.
