There are a couple of big differences this time. The first is we are talking a major signature ride. I don't think Disney wants to make a big deal of it not being available to guests.
Didn't they announce the Haunted Mansion refurb well in advance? (On our first trip, I got to ride it the day before it went down, so I remember knowing about it in advance.)
ETA: Just checked on Doombuggies.com; the 2007 HM refurb was announced in March, and began in June. I would think there'd be at least as much lead time for Space Mountain.