I am of the opinion that if you make a game for the hardcore, the casuals will follow. The reasoning being that hardcores are very demanding of quality, so if they like a game, everybody else will.
Don't be scared of being labeled "niche". If your game has an accessible UI (like all Worms games), lots of features (like most Worms games), and a flashy presentation (like most modern games), people won't be scared to try something with deep, competitive gameplay - see Rocket League.
A warning, though. This website in some ways represents the worst of Worms. We are the hardest of the hardcore. A veritable in-crowd. You will hear a lot of "just make WA 4.0". And that's certainly a good thing. If Team17 could somehow assist Deadcode & CyberShadow, that would be awesome.
But although WA's gameplay may be near perfect, it's an old game on an old engine with old sensibilities. A proper sequel to WA with the flexibility and consistency of old, combined with the technology of today, would be fantastic for everyone.
Study this thread. Study what people love about WA and hate about...pretty much everything after it (sorry). Ask questions. And above all else, don't be like the previous community managers that Worms fans have nothing but contempt for for being pretty much just a marketing department. We'll respect you if you respect your base (won't we, guys?).