I think each land needs to try and accommodate in some way for all ages (besides young children which isn't always possible when they have their own exclusive lands anyway), but Forbidden Valley has The Blade for families and well not short of thrill rides, X sector seems to be exclusive to thrill seekers at the moment so possibly needs something along the family lines to replace Submission. Dark Forest is crying out for a flat ride. If Adventure Land is to be a land it needs more than just Sonic Spinball! Gloomy Wood has always seemed a bit pointless as a one ride land, and as a rollercoaster isn't practical at least needs a flat ride of some sort. I've listed them in what order I think there will be some change. Katanga Canyon ideally needs a flat ride.
SUBMISSION (Replacement): Couldn't have guessed the ride would have been removed just yet, although don't think Alton knew either as they probably came across a problem not worth keeping the relatively unpopular ride. I personally would like to see, which may be a controversial choice due to its low throughput but if Chessington, Drayton Manor and now Thorpe can have one, is Dodgems/Bumper Cars!
ENTERPRISE: I don't really want to see this ride go, even though I rarely go in it due to it being amongst the few rides that make me feel sick, it fits so perfect in the banked turn on Oblivion and really would be a shame to see it removed and what could possibly go there... which is where i think if Enterprise was to be removed, it could be combined with the (now free) area of submission for possibly a Disk'O coaster, or some larger flat ride.
RIPSAW: If the cross valley coaster of some form ever happens, then I'm guessing this area will probably be used... if not, I can't necessarily see Alton replacing it with another top spin even if the new version is slightly different with front and back facing seats. In terms of timescale i could see it being removed as early as 2016/2017, but honestly not sure what to be replaced by.
ADVENTURE LAND: The future of this area is dependant on the future of Sonic Spinball as no-one knows how long it's going to stay, and as it is originally quite a cheap ride investment, and apparently not too keen on it spoiling the view from the entrance looking at the towers. But if sonic is to stay it seriously needs a flat ride in the area of some form, most likely a family thrilling one (just like Sonic is as a rollercoaster) - or alternatively be an add-on to Cebeebies Land as CBBC, with Sonic getting a retheme and a flat ride to be added. Most likely it will be left as it is for the next few years and will probably get removed/moved, and Cebeebies Land expanded which seems a pretty obvious choice.
THE BLADE: If I'm perfectly honest I find it the most boring swinging ship I've been on, but the location for it, is perfect for what it is, and would happily see it replaced with another swinging ship when the time comes. I personally would want it to be replaced by a ride similar to Vortex at Thorpe Park or Maelstrom at Drayton Manor, which I guess is totally plausible even with the height restrictions, due to it being in a ditch - alternatively this little valley could possibly fit a Zamperla Disk'O Coaster.
GLOOMY WOOD: Duel as a standalone attraction in the land is a bit pointless, although I think the theme of the area itself is great could just do with squeezing in a flat ride somewhere... would love to see a Huss Breakdance come back to the park.
DARK FOREST: I wasn't too sure where a flat ride would fit in Dark Forest, but it certainly needs another attraction besides rollercoasters; i did see on google maps and was surprised how large the picnic area is, and if they could create another entrance to dark forest down that end as well as having a new flat ride there. What I thought would have been good, would have been the Twirling Toadstool (with the ride being themed to a tree) to be in Dark Forest with the added Water Effects like Monkey Swinger at Chessington to make the ride more interesting although the water effects should probably be toned down and on more of a spray setting as they do get you soaked! I remember seeing a concept (whether it was genuine or not) for Robot Arms to be in Dark Forest which would be amazing but at such a high cost for such low throughput almost seems a stupid choice! Either way some form of flat ride needs to belong in Dark Forest!
KATANGA CANYON: unless they intend to build a new coaster with the station area being between the Congo Rapids and The Flume which goes over Katanga Canyon, that plot of land mentioned could be put to good use with a flat ride, although would require a pretty long path to get to from in Katanga Canyon!
FORBIDDEN VALLEY (Air / New Entrance): If this new entrance goes ahead, which would create more room around air, I would love to see a Gerstlauer Sky Roller or Sky Flyer next to air as it fit's in with the Flight of air over the Oasis area at the other end of Forbidden Valley which really needs to happen after being scrapped.