Hi!
it certainly can, but does it?
Just see the source:
https://github.com/melisgl/named-readtables/blob/master/src/named-readtables... in-readtable calls %frob-swank-readtable-alist .
and if it does, then why?
I don't know, but I think it was done for some purpose and something may depend on it.
let's change it so that it doesn't alter *readtable-alist*!
This seem to be ideal solution at a glance, but I think we should find the reason why it was done this way initially.