In a perfect world, they'll keep the recent UT's aesthetics (Gears of War-esque) with the fast paced ridiculousness of UT99.
Personally, I'm one of the very few people who actually liked UT3 (post Titan patch), it had some neat ideas going on and it still kinda retained that old school flavor (as old school as you could get in '09 at least), some modders even went as far as creating mutators that sped up the game signifficantly and they even remade some of the older UT99 maps.
Also, that "levolution" thing of BF4?, yeah, the UT series did it first (don't know specifically wich one started it, but I'm going for UT3).
I appreciate each and every entry on the UT series (strictly speaking of 99, 2K4 and 3), each and every one of them brought something different, perhaps '99 might be the best out of raw and pure break-neck speeds and sheer amount of content and fun (dem bots... they don't do them like that nowadays), so I hope that the new UT picks the best aspects of each game and improve upon them in some way.