[tel]

There has to be an RTS interface. Right now this is "there exists a value called main in the Main module of type IO which the RTS magically understands". This is annoying because it moves so much of IO's reasoning into "RTS Magic".

There are better models of IO (some discussion here http://comonad.com/reader/2011/free-monads-for-less-3/) which essentially boil down to "bidirectional communication channel with a Real Machine" and these can provide a foothold for better semantics. Similar ideas drove the first "IO" based on input and output streams (but handles synchronization the way we need).

There's also chance for other ideas of RTS. For instance, we might embed 99% of Haskell into a real-time RTS and have real world interaction be governed by something like FRP.