I half suspect the next tallest full-circuit coaster in the world will be Steel Dragon 2000. Both TTD and Ka are insanely expensive to maintain, and sooner or later, keeping them running will cost more than they're worth.
Though, as stated this is only a half suspicion. After all, we're talking about many years in the future. Perhaps the entire launch sections of TTD and Ka will be replaced without anybody touching the tower. Perhaps the coasters will live on with new trains and completely new electronics. Perhaps SD2K will be torn down first, or some Chinese park builds an actual Teracoaster (Lift hill coaster taller than 100 metres). Either way, I doubt another Stratacoaster will be built in the immediate future. I don't think aiming for the height record is profitable any more.
As for the speed record... well, there are lots of possibilities. Perhaps the launch of the next speedster will go in a wind tunnel to decrease air resistance on the train. Perhaps they finally get the railgun launch to work properly. Or they might reuse energy from the initial launch when braking it down immediately after. Let's face it, it isn't at all profitable to break the speed record and then have a full layout without trimming. To avoid excessive stress on the train and track, you need to kill the speed somehow before going lateral; TTD and Ka achieve this by launching into a steep incline, which handily enough also turns the train around (so you don't need the equivalent of a full air strip length for the coaster). I think "launch, then brake, then layout" is the future for all record breakers, or for that matter all coasters exceeding 200 km/h.
I'd love to be proven wrong, though.