Hey Myles,
Yes, I find all these alternate formats interesting. That's certainly one of the advantages of analog,.. you don't have to start from scratch to test these alternatives out. Most machines have speed adjustments and, at least as far as ips goes, you can try it for yourself with some fine tuning to the record and repro electronics. I'd hate to think what it would take to try an entirely different sample/bit rate.
I think that slitting a different size tape width would be more of a matter of changing the position of the slitting machines cutting discs and having 3" hubs for the reels made.
You question did remind me that I've been meaning to try and get a virtual tour or video of ATR Magnetics tape production facility. IIRC, when Mike Spitz was still in the process of getting all his ducks in a row to make his new tape available, his website mentioned making a video tour available eventually. I'll shoot him an email and maybe we can at least get some pictures of how tape is manufactured (maybe pictures are available in some books somewhere, but I've done quite a bit of searching on the web and I've never found anything).