Right now these functions accept a variable number of arguments and produce a tight packed version.

Some warnings are already displayed for tight packing literals. #982 proposes to turn those warnings into errors.

The new abi.encode*() methods offer a replacement to perform packing, which then can be passed to all these hashing functions.

Proposal is to raise a warning now when these hashing functions receive multiple arguments or the first and only argument isn't of bytes type.