Whatever the case may be, TF should avoid 15+ min time to next block situations. CfB already hinted at this, the high variance from willy-nilly needle in a haystack random hashing, and using base target to compensate, eventually leads to potentially catastrophic situations like multiple quick blocks followed by an insanely long one.
I'm not sure how Nxt avoids 15+ min blocks either. My info is a little hazy and the OP of this thread and the other linked do not clarify much, but forgers who miss a block are penalized for 1,440 blocks or something I think. That's not a big penalty, especially considering that there may be millions or billions of accounts and your odds of being selected again in those next 1,440 blocks are low. A choice of 3 forgers does not really improve things because all it does is take a big number and divide by 3. The number of potential forgers can't really scale up because then you have many multiple accounts competing for the same block which would be pretty disorganized and would not lend much weight to early transaction confirmations. So if you keep it low, you are hoping that some few specific accounts are all online and ready to forge. Needle in a haystack here too? Maybe.
NXT forging is deterministic, we are not searching for a needle in a haystack. Even with 1 billion forging nodes, you will know with 99.99% (or something close to that) accuracy the next X people that will forge. In the future, base target (difficulty) will simply be a legacy from Bitcoin - which c-f-b mentioned in OP - because why do you need to adjust difficulty when the forging order is already determined? If the order is determined, you simply say "X, broadcast your block at 60s, otherwise you will be penalized." 60 seconds later, "Y, broadcast your block at 60s, otherwise you will be penalized." And so on. In this scenario, X and Y are groups of forgers.
Anyways, I won't claim to understand how any of this works, but the important concept to understand is that forging is deterministic, thus you can have blocks come out in exactly 60 second intervals.