Re: Is this the expected behaviour for nameref in Bash 4.4 now?

[Dan Douglas]

Yes that was an intentional change to require valid identifiers. I can't
say it will always be that way or that there won't at some point be a
workaround. You can stiill use `${!param}' for now to refer to positional
parameters as you always could, but as usual that isn't useful if you
want to assign by reference.