We don't have anarchy, we have a light handed dictator who trusts his subjects to be civil and even tempered. A small amount of disorder is the price we pay for our freedom.
In the spirit of that, I'd like to see category tags in more thread headings (I'm using one here), but I wouldn't want to see them made mandatory. That would just be one more thing for the less cool headed folks to rave about, while the actual benefits could be achieved without a hard and fast rule.
If we, as civilized people working towards a common goal, can each of us resolve to try to do whatever we can to keep thing organized, without behaving like dicks, I believe that we can do that.
As to megathreads. I don't like them myself, as it's an enormous pain to find one conversation, in the numerous conversations that go on in a single megathread. If you keep up with the thread as it develops, it's not a real problem, but reading old megathreads is a big headache for me.
With that in mind, I propose optional Indexing Threads. These would serve the same organizational purpose as as a megathread, with a starting post full of links to particular topics. However, the actual discussions would still take place in separate threads, so a new idea won't derail the current conversation, or cause confusion. The OP of such a thread would be responsible for adding new threads to the lists, as people post in the thread asking to have their ideas indexed.
Because these systems are entirely voluntary, they adds no burden of enforcement at all. The systems could be implemented without any effort on Toady's part, whatsoever. It's just something we could do to make his job easier, and allow everyone to find what they're looking for, faster and easier.