Anthony, this proposal is to remove the Eq and Show constraints from the Num class. Specific instances of Num, like Int and Float, will still have those instances. This has been how it is in GHC for a long time now, so it really is a matter for the Haskell' committee rather than one of the GHC committees.
The motivation is that there are many types with sensible definitions for addition and multiplication etc that can't be instances of Eq or Show, for example functions to numbers (allowing us to write "sin + cos" instead of "\x -> sin x + cos X") or arbitrary real numbers (where comparison isn't necessarily computable).
I'm not sure why this is being discussed on the mailing list rather than the Github proposals thing, but I do know that that has grown somewhat inactive and this is as good as anything for getting the Haskell' committee to make a final judgement.
Nathan