Hi Holger, hi all
Overall I think restricting the user and index names is the proper way to go.
On our installation we are using the dot (.) in addition the characters suggested by you. If that character would no longer be legal in 3.X this would make the migration rather painful for us, as we store references to the indices in external systems. Thus, we would require names matching following regex to be valid:
I am not convinced that mangeling would work to well for us, as it would increase the amount of requests performed during `pip install`, causing a lot of additional traffic and load.
Kind Regards, Matthias