Season 3 has:
6 Malibu Sands episodes
26 Bayside episodes (counting the ones that most people label "Season 2" that aren't included).
That will take up 5 discs, at least, like the set that's been released.
Season 4 has 22 episodes: 11 episodes with Torri and 11 episodes with Kelly. That's 4 more discs and they can throw on the Hawaiian Style movie too.
They might be better off just releasing Seasons 3 and 4 separately, then. And then a 2-disc Good Morning Miss Bliss set, a 4-disc College Years set (3 discs of episodes + the Wedding in Las Vegas movie).
Now, assuming they go and actually give us extras, they'll want to keep the maximum number of episodes per disc around 6, I'd think.
I really don't care how they do it, just so long as we get all of the episodes, for a reasonable price, and in a timely fashion. And extras would be nice.
Then again, NBC apparently has an odd order to what they consider 'seasons' - in which case the number of episodes would be entirely different. Perhaps this is what has been meant in the descriptions that state, "For five seasons." They might be counting the Torri season and senior year with Jessie and Kelly as two different seasons. And then Season 4 seems long, because they count what most consider the second half of Season 3 (all the Malibu Sands episodes and more) with that. It's confusing, but this kind of helps a little bit in the NBC way of thinking:
http://homepage.mac.com/ijball/SbtB/Ordered-List.html