In general, as long as delimited argument matching is used to parse the value list, redefining catcodes of list syntax characters will be a problem (same for LaTeX lists).
One could redefine
\pgfkeys@@set to re-catcode
= like this:
I'm not getting much of a test result as your MWE doesn't produce any output, but at least I'm getting no errors ;-)
Don't know whether this was the kind of general robust solution you're looking for though...
Please see the comments below on why the above is not a good idea.
\scantokens will de-activate all instances of
= in its argument, also in the values of keys where they need to be active to fulfill the purpose they were originally made active for.
Following the comment of Joseph Wright below, here is a "solution" referring to the
kvsetkeys package (Which was, obviously, an enormous tedium to make. Kudos to Heiko for this achievement!):
Again, I'm getting no errors :-)
I'd be interested to hear what the drawbacks of this approach are.