If it has less than 64 kB of memory how is it going to run a WASM runtime anyway?
And even cheap microcontrollers tend to have more than 64 kB of memory these days. Doesn't not seem remotely worth the complexity.
We're working on WASM for embedded over at atym.io if you're interested.
There is WARDuino (https://github.com/TOPLLab/WARDuino and https://dl.acm.org/doi/10.1145/3357390.3361029).
A runtime that accepts Wasm modules that use a large fraction of the functionality, there is going to be a RAM requirement in the few KiB to few tens of KiB. There seems to be a branch or fork of Wasm3 for Arduino (https://github.com/wasm3/wasm3-arduino).
If you are willing to do, e.g. Wasm -> AVR AOT compilation, then the runtime can be quite small. That basically implies that compilation does not happen on device, but at deployment time.