Has anyone ever built a bridge pickup with a ceramic magnet on the wound strings and alnico 5 magnet on the plain strings? Is that even possible to do with 2 different magnets?
People have made pickups where they mix A2 and A5 for that scenario, so I magine doing it with what you described can be done as well. 3rd Power might do a Magfrag for you with that config.
I've been LITTERALLY thinking about this all week. Personally I want to add some A2 spacers to the non-wound strings to soften/thicken things up on solos for the A8 pickup I have. Though also considering just doing a full A8/A5 split and then a ceramic spacer for just the A5 strings; this is where I need an expert to weigh in (or have a lot more free time to break stuff myself).
From my research, there's only a handful of builders that have a product like this (and none that are explicitly what you asked for). You have to be careful mixing ceramic and low strength alnicos as there is the potential for degaussing to occur. Also volume difference can be an issue depending upon the magnet type.
It seems to me like the already lower-mass strings would not be helped by being paired with the lower flux magnet. Unless the goal is to get it to sound more like a 3-string guitar.
I had Jalen make me a set of single coil pickups with A5 for the wound strings and A2 for the unwound strings, best single coils I've ever used, I'm sure it can be done on full sized humbuckers, hit him up!