How hard can it be to add what the stuff people liked from UT1 (UT99 if you want), UT2 (UT2003/UT2004) and UT3 to a possible UT4.
Gameplay of UT1/UT3, a mix of weapons from all 3 UT's. UI based in UT1 (or even UT2), the most played maps from the other UT's, this would avoid developing new stuff (would save time and money) and make people happy!
SP would actually be a tournament that you have to win to save your race (not a race, has in racing). The story would be something like, while trying to win the battle (UT3) no race was able to get an advantage, with that in mind they choose their best warriors to participate in a new tournament that will decide which is the best race, Humans(Ronin), Necris, Skaarj(Krall), Liandri(robots o/). With this 4 teams you could even have MultiCTF, MultiDM, MultiONS(warfare) games, etc... This would allow to promote even more the new engine (huge maps with 32 players, 8 for each team)
You could add a new MP mode, like a race (racing with cars), where you have to go from point A to B (passing some control points in the middle) and use the weapons in the vehicles to make the other vehicles crash. Manta's races, Hellbender races and even some Goliath races eheh Mario Kart style lol
I could keep on going..
Epic if you want more ideas pm me, i have dozens more, contact me! :d