Well, all technical considerations aside, well-loved films that are no longer available in sheet film, but "old school" in make-up would be such films as DoubleX, PlusX, PanatomicX. perhaps soon to be gone Tri-X.
Aside from bringing back Polaroid Type 55, I'd agree with Greg, and say there's a void to be filled in high-speed, fine-grained colour negative film for LF.
Maybe 800 or even 1600 ISO.
I would recommend starting with a b&w film, ISO 200 to 400, that is relatively "easy" and "economical" to manufacture. Concentrate on super quality control and build a customer base of enthusiastic, satisfied users. Then branch out to other speeds following that same mode. Let your b&w sales justify the move into color.
Wait a few months and you may be able to buy Kodak's film operations for a song.
Whatever you might produce, it needs to be just as good as or better than any current product from the three major manufacturers, it will need equal quality control and consistency, and must be competitively priced. If you can't meet these criteria, photographers will substitute the nearest equivalent film from another manufacturer.
Anything less will put your products into the realm of the second-tier manufacturers, whose products often present a perceived quality risk only the price-sensitive want to take. You will be hard pressed to compete on price, since these manufacturers are well-established. If these manufacturers produce your film for you, you share the public perception of their products and the perceived quality risk.
Remember that the cheapest part of any photographic undertaking is the film. Few experienced film photographers will risk potential film quality problems over proven performance.
All good so far. It sounds like there is a market for certain types of film.
Just to add, right now I am only doing market research to determine if making film is profitable venture.
As of now I plan on making a few B&W emulsions to test. Hearing what you have to say is helpful in determining what I should make.
The best thing I have going for me is that my R&D cost will be almost nothing. I have full access to all the lab equipment I will need, plus a low cost chemical supplier.
Keep your thoughts coming. The more ideas the better.
I'm happy with my normal B&W film choices. Unusual is the place to build a new niche market.
I'd suggest helping out the new55 project... Or a IR film, or a 4x5 film with the same spectral response as pre-panchromatic early 20th century look.
"If it is something akin to the characteristics of PlusX or SuperXX I'd buy!"
If you could make T-max 400 with the spectral sensitivity of the classic X films it would be fine. Having a shoulder to the HD curve would not be a bad thing.
Scan-able, wet print-able and no UV blockers for alt process.
Grain, it's supposed to be there.