Note - I pretty much drifted away from photography in 2013-ish, got interested right after my divorce in 2015 and stocked up on paper and chems, then didn't really do much with it. So it's been nearly 10 years since I shot film even half seriously. From that perspective:
Interesting, to me anyway, to see the calls for faster-than-400 color films. To me, digital has pretty much nixed the need or even desire for that. It just does very low light so much better. I hate to admit that, because I do photography because I enjoy it, and it's much more about the process than the artifact for me, and I just don't enjoy working digitally that much, but it's true. Black and white is, maybe anyway, a little different because of the look of real grain versus digital noise. You just get a look with high speed ( > 400) black and white films that I've not quite seen from any digital. But we have TMZ back, something I NEVER thought I'd see and am very glad for, as well as Delta 3200, the latter in both 35mm and 120, which sorely tempts me to find an 80 f/1.9 for my Mamiya 645 Pro.
Ektachrome 400 would be welcome, at least to me. I still have a stash of frozen Provia 400X but frozen film stashes are never enough film, and I don't know how well it's kept (probably well enough.) It seems maybe within the realm of possibility so I would like to see Ektachrome in 400. Faster would be welcome but in the past the faster than 400 color films I've shot have not impressed me much (exception - Portra 800, and unlike a lot of folks I preferred the results from it to those from the 400 underexposed by a stop, with or without pushing processing. It isn't great, but it is pretty good, and often that's good enough.) I don't see the need for a VERY fast color film anymore given just how much better digital can do at those speeds, but 400 is a very "comfortable" speed for me for regular shooting, much more so than 100. We have 200 and 400 in C41 but it would be very nice to have in E6 again as well.
What I'd REALLY like to see is a good color film in 4x5 sheets at a much less outrageous price than today's sticker shock inducing ones . If we can get Kodak's 120 C41 films at $12 a roll or so - expensive, even a bit of a shock returning to photography after several years away, but still something I can afford to shoot - we should be able to get the same films in 4x5 for $3 a sheet. Heck, Gold 200 is $8.99 a roll (all prices from a quick look at Freestyle just now) so given a 4x5 sheet has about 1/4 the area of a roll of 120 that'd be more like $2.25 a sheet. I know, I know - it's a very different film base, much less economy of scale etc. But it also doesn't need backing paper or film spools and I can dream, can't I? As it is, my return to photography will mean color is limited to my medium format cameras or in cases where I really want view camera movements a roll film back on my 4x5.
The same reasoning applies for me to E6 film in sheets. We have Provia 100 and Ektachrome 100, but both are around $6 a shot in 4x5 - pretty prohibitive, especially when I can get a 120 roll for as "little" as $13 (Provia 100, 5 roll pack is currently $64.99 at Freestyle, expected in stock Aug 5) and get 10 shots from that with my roll film back on my 4x5, or in my RZ 67.
While I'm semi-ranting about cost, how about a good black and white film in 8x10 that doesn't break the bank to shoot? I'm interested in dabbling in 8x10 but if I do that's going to mean x-ray film. And given how medical imaging has gone, if I do that I'll stock a small chest freezer with the stuff if I can dial in results that suit. 4x5 I can still, sort of, justify shooting, given how slowly I work in 4x5 anyway.
I'm about a 90% black and white shooter, but those comments are all about color with the exception of the bit about TMZ and D3200, but that's just because I'm pretty happy with current offerings in black and white. Maybe, as others have said, a real infrared film might be fun. Other than that, we are fortunate to still have a pretty vast selection of good black and white films on the market already.