The thing is 3 tags feels like the default to me. 1 tag is beginner mode (very easy), with 2 tags the possibilities are still huge (easy), and 3 tags feels comfortable (normal). So I kinda feel I'm missing a hard option.
But maybe that has to do with me being an avid user of the tag connecting tool. I've gotten used to thinking up design concepts with more than 3 tags. And every now and again I get a group of 4 or 5 tags that would really work well in a session together. Such as:
[Character] Hooded ~ Hunter ~ Experienced ~ Marks ~ Whip
[Environment] Market ~ International ~ Cheerful ~ Gold
[Creature] Psychic ~ Float ~ Deadly ~ Squishy ~ Mask
[Scene] Confined ~ Empathy ~ Sorrow ~ Blood ~ Touch
[Vehicle] Dig ~ Laser ~ Cargo ~ Fumes
As for the design issues, I took a look at public and personal galleries, and for every 3 tag piece it looked like the current design can handle another long tag added to it:
Maybe it didn't fit earlier because you were still using the old tag system that allowed multiple words, or maybe you made other changes since then, but it looks to me design-wise it's not much of a problem in the majority of the cases. I guess it could still go wrong if you combine 4 of the longest tags we have, but I think the chances of that happening regularly are not too great.
I would also really like to try out a session with 5 tags, but I can understand if that's too much.
Oh, but I just realized, at the tag connecting tool I have a personal database with thousands of self submitted tag connections! If I want to try sessions with many tags I can just pick 3 tags and use the magic of ctrl+F to manually "generate" the remaining tags. I just might try that.