I started looking into this in more detail. This may turn out to be more interesting than my initial gut assessment, although it is still unclear in how many cases an actual new solution will exist from this challenge.
Basically I underestimated that in a lot of the 1-minute solutions to easy levels, they may be trivial to merely meet the minimum save requirement, but much more time constrained when everyone has to make it in, therefore requiring additional nontrivial techniques in this challenge. I have attached an example mentioned later in this post.
For rating Fun, I have basically now confirmed that other than the following two levels whose fate are still to be determined, the rest of Fun are either confirmed possible for the challenge, or "trivially likely impossible" (ie. no known solutions found even in the existing challenges relaxing either of the two requirements). The two levels left are:
Fun 16, Fun 29
I have attached replay to Fun 7 which illustrates the kind of cases where this challenge gets more interesting (and also often more grindy, unfortunately). That level is uninteresting for 1-minute alone or 100% alone, but with both together, you have to apply some extra techniques to help ensure everyone makes it in time to the exit. It is really the only level in Fun thus far whose solution for this challenge illustrates anything new for the level. In all other cases either the trivial solution will work, or the solution is more or less something you have already seen in other challenges already for that level.
For Fun 16, the situation is this: we know that its repeat, Taxing 3, is possible for 1 minute and already requires 100%. However the solution presented in the 1-minute challenge thread (from yours truly) uses more than 20 builders (Taxing 3 has 30 of everything except blockers, while Fun 16 only has 20 of each), so the solution can't be applied as-is to Fun 16. And given that the massive use of builders is fairly crucial to getting the path set up quickly enough, it might well be that there is no way to get it working with only 20 builders. So right now we just don't know yet whether it is possible or not.
As for Fun 29, for 1-minute Clam presented a spectacular solution using the sliding glitch, which additionally uses bombers as well for setting up the sliding. All that makes it almost certainly impossible to adapt for a 100% solution. It remains to be seen whether it is actually possible to solve in 1 minute more conventionally, but I would guess "no" if the only known solution at this point is a Clam solution with sliding. ;p
Bonus: Tricky 1--at first I thought it might be eliminated by showing the simply the walking alone would be too much. So I modified the level: fill in the gap, remove the obstacle, and sort of flatten out any bumps that would've cause a walker lemming to transition to jumper or faller. But as it turns out, with those changes the lemmings can actually make it in time with around 1 game second to spare--if the pause glitch is used. But, in an actual solution the gap has to be built over and the obstacle bashed through, and especially with the builder we know it takes something like 10 frames just for the build brick to actually materialize in the level, so with 1 game second equal to 17 frames, most likely there still won't be enough time even if you use all the time-extending glitches at hand (eg. the fade out in high-performance mode in real DOSBox Lemmings). Mind you I haven't carried out any actual measurements and calculations yet so I'm not 100% certain, but otherwise I'm leaning towards "not possible" for now..
