You would have to ask the dev's but i would think an LFS 2 would be more likely than S4 - you can only develop so much before you need a fresh(ish) start.
Still like i said this is one for the dev's, i don't wanna start any rumor's flying around!
Originally LFS was meant to be released in 4 stages, so an S4 was planned but it was limited to three. And afaik what happens after S2 is not sure either. There's a possibility some other form of releasing will be used, Scawen probably hasn't made any decision on that. And I doubt he will before S2 has been completed.
I wouldn't worry about it because as you say there's still a long way and years of enjoyment to go.
And are those exclamation marks really necessary?