I could see Universal doing it in phases like Disney did with the New Fantasyland
Phase 1 (Fall 2013-Spring 2014):
Animal Actors upgrade
Fievel demo/replacement
E.T. Entrance relocation
KidZone Pizza replacement
Phase 2 (Fall 2014-Spring 2015):
Addition of a few flat rides
Barney demo (Scooby dark ride in its place)
Phase 3 (Fall 2015-Summer 2016):
E-ticket SpongBob dark ride
Curious George relocation
Unknown kiddie IP attraction
Woody Nuthouse relocation and theming upgrade with extended track
Looney Tunes boat ride (either outdoor or indoor)
However, Comcast wouldn't do the grand opening until everything was open (to avoid "dwarfing" their big project lol)
It makes sense for a drastic renovation to only close a few things at a time to avoid bottle necking the one family area of the park