5bld has the fewest competitors of all 17 events, followed by 4bld. MBLD has more competitors than both combined. Even 3x3feet, which hasn't been an event in 5 years, still has more competitors than 5bld or 4bld do now.
7x7 has the fewest competitors of all 11 puzzles, followed by 6x6. 3bld has more competitors than both.
You have to draw the line somewhere at too many events, and the ones with the fewest competitors are the best candidates to get rid of, especially when they're just "bigger and more of the same but take longer", which offers absolutely nothing new.
I think Mirror cube would be the most likely for a new event, then maybe FTO.