Hi! For what it's worth, your handpainted texture pack is the first one I search through when making prototypes or 3D jam games. They're really pleasing to the eye, and I can usually find enough variants to make the game come together. My only complaint is I had to download each pack by hand, but that's on itch :P.

As far as old-school doom-like sprites go, if you want to provide really good ones for creatures, then they require each frame to be drawn from multiple angles. That's a lot of work, so keep that in mind. There have been a few succesful games lately that used this rendering technique (sprites in 3D environments) - Forgive me father, Project warlock, Nightmare reaper and so on. If other devs were to follow those games, then you might find customers there.

Honestly, I love your work. I've been eyeing them for such a while now, but I've never committed to buy them yet simply because of time restrictions, and my obsessive need to collect assets and never use them and a fully completed project. Because I know once I start purchasing it's going to be in binges.

I think moving to a pixel style would be very good shift, especially since this renaissance of N64 PS1 style graphics is really in vogue right now. I'm also from the RPG developer Bakin community and the main reason I've been eyeing your work is because it's very applicable to that community. Bakin community needs assets like you wouldn't believe. And many can use your texture talents in making HD 2D/ Pixel HD Assets environments and environments, as well as the hand painted stuff you already got going. You have no idea how hard it is to look for the stuff that you make. Usually I have to resort to tile sets and then retrofitting them into textures to wrap around 3D models. A perfect example would be on my itch.io page, the Adventure field demo is made up of textures that I made by editing tile sets made for RPG Maker Style Games. 

I think your work is really important and probably you can alternate between the two. The hand-painted stuff and the pixel art stuff to give yourself a wider range. You do have a lot of ye old things too, Why not branch out into some modern textures or futuristic textures. There aren't a lot of those on offer. Building walls, windows, Ship hulls, Factory floors, Cyberpunk interior textures, Alien exterior, interior textures, Those sort of things. And again you can always have a pixel version for those that want to do HD 2D and you can have the hand-drawn version for those that want the cleaner art full look. You can even get little res with it as well. Make a pixel version, an N64 res version, and an HD version. So instead of the 300 of one style, it would be 100 of each style in one pack. That way you can keep your creativity going, expand, and eat. You're not dropping one for the other. You're broadening your categories. 

Well, that's my take anyway.