Just like in almost every sellable item theres a Vintage version of it or of its kind so there is to a market for "vintage" video games.
Simplicity almost everytime is everything, and in games is no exception.
This type of games are refreshingly welcome in a -FPS HD on rails saturated everybody does it but almost none does it right- market.
But make no mistake, the todays audience wants innovation so if they want to make this kind of game definetly they need to add todays kind of features to yesterdays kind of game.
In my opinion there should be more interactivity with the game itself, ledge grabbing jumps, throwing objects, the goddam MightyFoot that i so miss in every FPS i play, rpg features like character,weapon customization even if minor, that cave,house,den,village kind of thing where you can get your missions, buy&sell, interact. Oh and if this is to be a Duke alike then make her a pottymouth, extreme feminist, oneliner, ballbuster kind of woman.
Dont get me wrong, i do love oldschool kind of games, but it is a major letdown to be just another throwback shooter.
Make it stand out. Make it immersable because that is what makes everyone love it and come back for more- immersion and customization- Giving the character life, making us care for the character and the story, and please a todays artist synthwave soundtrack, will do the trick.
Take hints from the great ones, system shock-deus ex-duke nukem 3d-blood...
For the place that this game whats to take in video game market, in the current state, there are bigger,better and cheaper old games to play, so if it comes to be just another one it will fall flat.
But that its just my opinion.
Anyway, love what you do and honestly wish the best of luck to the new 3D Realms.