I think that mines are one of the greatest things about JK. I can't see any reason to not have them in JK2. Mines teach awareness. If you are a very aware FPS player, mines are nothing to fear. Besides, where would we be without MJing, TeamMJing and stacking 30 mines on top of eachother for some mega-explosions. Mines are one of the only weapons that enabled you to kill Conc-holders in Oasis very easily(if you didn't have a Conc). Mines are very good for balance.
We need something with splash damage too. Mainly because games that don't have Rocket-jumping, simply aren't games at all. RJing, MJing and CJing in JK aloud you to take the game to levels that I don't think LEC ever imagined, especially in NF CTF.