They don't have intellectual progress as a goal.
The social incentives favor authors doing it more, and are ambivalent for the mods. Though I don't trust them either, particularly after such a massive failure of judgment as proposing this change.
Calling out obvious groupthink and bullshit. Which is depressingly common with increasing regularity.
I expect content's prominence on LesserWrong to be the result of political dynamics and filter bubbles, not insight or value. I do not expect it to be truth-tracking.
In line with this, I have given up on Lesserwrong. It's clearly not going to be a source of insight I can trust for much longer, and I have doubts that it was any time recently.
I am in the process of taking everything I posted here and putting it back on my personal blog. After that's been done, I don't know whether I will interact with this site at all, since the main contribution I feel is needed is banned and the mods have threatened to ban me as well.
Fix the links, not the limit.
So scale it to...the size it already is? Maybe double that? I don't think that requires any change. If you wanted a 10x user count increase, that probably would, but I don't think those 10X potential users even exist. Unless and until round 3 of "Eliezer writes something that has no business getting a large audience into his preferred cause areas, but somehow works anyway" occurs.
I am also extremely skeptical that any discussion platform can do the third thing you mention. I don't think any discussion platform that has ever existed both dealt with significant quantities of new people coming in well and was effective at filtering for effectiveness/quality. Those goals, in point of fact, seem directly opposed in most contexts; in order to judge people in any detail, the number to be judged must be kept small.
Are you sure you're not building for scale because that's the default thing you do with a web app made in the SF Bay Area?
Hmm, related question: Assuming this revival works, how long do you expect the site to be actively used before a 3.0 requiring a similar level of effort as this project becomes necessary? 5 years? 10?
(My prediction is 5 years.)
Why do you think that LessWrong can or should scale?
That is complete. I'm out.