Re: Gaps in the product line?
While this is a good question to ask every now and then, the other question that must be asked is "what pickups have you tried before answering?"
As well, gap has to be defined as a reasonable amount of demand in the general marketplace outside the 2-dozen on this forum (at most) that would seek out a Black Winter with a Tele baseplate, for example.
My guess is that very few people have tried the entire catalog of SD pickups through every type of guitar and amp combo, much less through the guitars and amps they actually have. It's one thing to say you want a pickup for x guitar into x amp for x tonal result, but if any one of those variables changes, you may find what you were looking for. It might be a Seth Lover in a maple Tele through a TripleRec, or a Distortion in a White Falcon through a JC-120. If you haven't tried it, can you really say it's missing?
With so many options for tweaking the tone through external gear (pedals, et al) as well as internal components (Varitone, et al), who can really say if there are gaps? As well, you still have traditional mindsets regarding guitars and amps and their associated musical genres, such as a Tele through a Tweed Deluxe for C&W or this or that through hither and yon for Death/Doom/Extreme Metals, and pickup form factors are typically limited to the perceived target audience, hence there's not as much variety in the lipstick or vintage Tele baseplate models as there are in Strat and Humbucker formats.
I don't see the need to explore coil and bobbin material differences. Copper is abundant and economical enough and an excellent conductor. While gold and silver may be more conductive, their tonal properties have yet to be proven, and the extra expense cannot be justified with a simple "just a little more" tonal result. Would a gold-coil JB still sound like a copper-coil JB? If so, why bother?
Magnet materials, however, could be interesting. ND mags are known for having a stronger field, so would it be possible to get the same results using half the standard number of coil wraps or less?
Pole piece shapes were mentioned as well. Perhaps a hybrid of a Quarter Pounder with Invader caps? Maybe one coil had QP slugs under 3 strings and standard slugs under the others? There were some thin metal shims offered in magazine ads years ago that were purported to alter the tonal response of a pickup - one model had diamond-shapes touted for a more aggressive response (for Metal/Hard Rock), and another had round shapes touted for a smoother, output-boosting effect for those low-output vintage pickups. I never found out of this was factual or snake-oil.
