Ah, here we go - from the FSM thread that first alerted me to it, I just found (and then remembered that I'd seen it earlier) the original source - John Williams fansite jwfan.net reported it
near the beginning of the month:
John Williams' score for Indiana Jones and the Kingdom of the Crystal Skull will be released on the Concord label on May 20, 2008. The company will also re-release the other three Indiana Jones soundtracks at a later date.
Well, there we go. Not much to go on, just yet, but there it is - rereleases at a later date (so I might've been wrong about "later this year
;" I'll try to remember whether I inadvertently made that up or got it somewhere else from some other source).