I don’t think we should do this yet.
I am not opposed to creating such a category, but to start I think it should be limited to TL3. While in principle I like the idea, and I agree that Snowdrift tends to inspire these sorts of conversations, tackling the problem of civil discourse is a massive increase in scope. Given our current resources, I think it distracts from our core mission.
Just because @Adroit and @photm are capable of having a nuanced discussion in text without much moderation, does not mean the internet at large is.
Given that #restricted:lodge has not seen much traffic so far (as expected, since not many people have TL3 so far), I am not sure there is value in creating a separate philosophy category…. yet!
I also think we ought to split the last few posts in On solving the world's problems, where the discussion takes a philosophical turn, into a new thread in #restricted:lodge.
As a compromise to keeping this type of discussion TL3-restricted, I think we should not hesitate to manually bump people to TL3, when appropriate. We can think of the default TL3 criteria as, “This is how much interaction we need to have with someone [on the forum exclusively] before we trust they can engage appropriately with off-topic and more-private conversations.” However, there’s other channels where we interact with people — matrix/irc, github, meetings… Discourse can’t know about those, but we can act on them.