Without a JIT, I don't see any much interest for WebAsm, to be honnest...
I know that https://github.com/wasm3/wasm3 projects are good enough to run most simple processes.
Having a Delphi version - sad it is not FPC compatible - is a good idea. Even if it is Wintel only.
In terms of interpreting some logic, with proper sandboxing, a transpiler from other languages to JavaScript could be of a better interest, since most high-level features (like object mapping/dictionary, or strings) are already coded in compiled/native code.
Since everyone is throughin away references, take a look at https://github.com/saghul/txiki.js coupled quickjs (fastest interpreter, but slower than Chakra, V8 or SM) and wasm3. 🙂
Edit: the FPC webassembly backend is more a proof of concept, just like the LLVM backend - on which it is based somehow, at least to produce the binary output. It lacks some pascal features, and is not ready to be used on any project sharing the same code than regular FPC pascal code. Also in this respect, the JavaScript FPC transpiler is much more advanced and usable.