The ride opened in Tokyo in 1983. It'll be 41 years since this ride opened and like MK, it has never been retracked. It received an update in 2007 that was very much like what WDW got in 2009 - all cosmetic to make it look more sci-fi futuristic, but no real change to the ride. Like WDW, it also does not have on-board audio for the trains unlike the superior Space Mountain versions.
I think it got to the point where OLC just said, Hey, we got 40 years out of this ride system and the Space Mountain brand is very strong. Let's knock it down and rebuild with a classy and faithfully inspired exterior design and give people a ride that they can enjoy for another 40 years.
Basically, the ride is past its shelf life and they are doing the responsible thing unlike TDO who seems to not care about MK's SM. One can be hopeful that maybe they will do something after Tron opens, but I wouldn't get too hopeful.