That behavior would be similar to that of the linux32 command on Linux.
Personally I don't mind; either way is fine by me. Would do others
prefer?
The question was meant to read "What do others prefer?" Assuming it was
still understandable, I interpret the lack of responses as a lack of
strong opinions. So I'll go with Adrien's suggestion and implement
setarch as a command that starts a given command (or shell) with the new
environment and not as a function that modifies the current shell's
environment.
