Recently a Youtube video reminded me of a game I played years ago called Advance War. It's basically a turn based strategy game with the simplest mechanics that you conquer cities on the map to generate income, make units in the factory next to your HQ and try to capture your opponent's HQ to win the game. I am fairly interested in this genre, and I think I could make something with similar mechanics and add more flavor to it (ex.different factions with different units, better map design). 

The question is, is there any people who are still interested in this kind of old school game?

I loved that game. A good similar game would work fine. But as Septopus says many ripoff that aren't fun to play exist.

Advanced wars was simplistic but still felt fair and the mechanics/unit strength/weaknesses felt realistic. Units each had a distinct function/role in the game and the different characters (and their special power) worked well too.

"Tiny metal" is a modern take on the genre. I tried it but it didnt really fly with me. Maybe I'm just older now

I think a simplistic, almost board game feel to it works better than a realistic, military simulation style (with loads of unit stats, different resource types, including upkeep costs, realistic vision etc). But it also depends on how slow you want to make the game.

I play the doom RPG because its got good replay ability and a great story. But if you wanna make a turn based strategy game make a game like final fantasy where your not limited to choices and can attack freely. Also make the theme different from other games, no one wants a copy ya know