if/else and switch as expressions: These are conceptually interesting things to support, but many of the problems solved by making these into expressions are already solved in Swift in other ways. Making them expressions introduces significant tradeoffs, and on balance, we haven't found a design that is clearly better than what we have so far.
I wonder what these significant tradeoffs are? if/else and switch not being expressions makes certain code really awkward to write. Luckily Swift doesn't force you to use mutability here, but it's still weird IMO.