Hardcore mode risks splitting the community and making balancing a nightmare if weapons and/or tools differ from the standard game.
My suggestions as hardcore mode options that wouldn't affect wider balance issues but would increase the challenge of the mode..
- Friendly fire set to ON for both weapon damage and collision damage. No more risk-free shooting through your team mate or danger-close AoE barrages. It's frustrating when you're toe-to-toe with an opponent and their team mate is firing hwacha barrages into the fray from range without risk to their own team mate.
- Map location indicators for own ship, all other ships and all CPs set to OFF and HUD direction indicators set to OFF. No hints as to your team mates position so you'll need to know your maps and map reading to meet-up or to find a CP.
- Shake spot sensitivity increased, making it easier to shake spots. To make crews work harder to hold a target spotted.
- Mid-game join set to OFF. Predictable crews throughout the game. Or make the mode only selectable in a password match.
- Suicide set to OFF, ie. any ship death counts for the opposing team. This would probably be needed anyway with friendly fire set to ON.
- Selectable win-criteria. Allow first-to-seven for 2v2, allow other criteria such as first-to-three-with-two-points-clear-or-until-two-points-clear.
- CP randomiser for progressive CP matches. No more, "60 seconds left on B, I'm heading for C". Make it wait-and-see for hardcore CP matches.
Built-in single ship scrimmage support would be useful, but probably outside the scope of this thread.