They’re just different permutations of where you could stick eWASM and the EVM during a transition period. Not all of them make sense, but are there for completeness.
Run them in parallel
Have an EVM hosted on WASM as a precompile
Add an AS_WASM opcode to the EVM spec; accept WASM bytecode as args
Have WASM as a precompile in an EVM environment
Write an EVM in WASM, and use that until ETH 2.0; then use it in option 2
Drop the WASM idea all together and just improve the EVM
Drop the EVM completely; find migration strategy (transpile or manual migration)
OK. And there is 8–do nothing. And 7 can’t happen because existing EVM code and the code it generates must keep running. The rest are pretty much just different ways of implementing a client–unless we go with 6 or 8 then clients need to run both eWasm and EVM somehow. One way to make that easy for wasm-only clients–which might amount to 7–is to place a canonical evm2wasm transpiler on the blockchain for them to use. (This might also be a convenient way to compute gas for EVM operations.)