What do you mean? At the moment, you have two (backend + frontend) or three (backend, shared, frontend) modules, the first is a Kotlin JVM module, the latter a WASM module and you want to merge them into a multiplatform module with a JVM and wasm target?
I never did this but should be technologically possible.
On the other hand I prefer separate modules which makes the gradle setup less complex and the complication much faster due smaller sizes and less abi changes.
Additionally you need to run the compose compiler only on a subset, the wasm module, until there will be an option to exclude Kotlin complications, like the backend.
I would only merge the modules if you actually need expect/actual. Otherwise use separate modules.