I'm ambivalent, leaning towards not liking it. Though I only glanced through the thread.
When I was first playing getting to my first season change as a newbie I considered a major accomplishment and was motivation to keep playing. At 91 day seasons I could see newbie me considering it an unreachable goal, even now as a player that knows what they are doing I rarely get 90 days in before I get bored run out of serious threats and feel there is nothing further to gain from the run. I also see it as less likely anyone will want to experiment with animals or plants, as they likely take significantly longer to yield returns. If I understand correctly construction speed is also tied to season length? I can't see constructions taking longer than they already do and still being bothered with, but I may be misinformed there. It sounds like quite a few systems in the game would be made too long term to ever want to deal with by multiplying the investment time by something like 6.
On the other hand it is probably easier to code for real season lengths, and finding and crafting winter/summer gear will be more worth the trouble, foraging seasonal trees and berries would be more worth the investment at least in your current season, and it may open the way for seasonal zombies and animals, which would otherwise not be around long enough to ever bother with. That could even solve the 90 day boredom if new threats or goals could be introduced seasonally.
Again, leaning against, but not enough to start screaming bloody murder as we are wont here. Feel free to correct me if any of my thoughts are misinformed.