Actually, this is not quite right. Since ghc would still ship Cabal (but

not depend on it), it would also ship its dependencies including parsec,
mtl and transformers. So they would need to be up to date and installed,
it's just that ghc itself would not depend on them.

If that's really inconvenient, it's plausible to have a minimal set
which is just the things ghc depends on, so long as what gets shipped to
users is the useful set, including Cabal.