Would there be a way for people who already maintain blogs elsewhere to cross-post to their LW subdomain? (Would this even be desirable?)

We would have to discuss this with people who run blogs elsewhere to find out what solutions would work for them. My preferred solution would be for people to import their old blog posts, and then redirect their domain to the LW subdomain. I do not know whether outside bloggers would find this acceptable. In some cases we may also have to consider the question of advertisement revenues.

Do you envision LW2 continuing to include applied rationality type posts? Does that work with "everything should work towards Aumann agreement"?

My apologies, I did not intend to declare that posts about applied rationality should be avoided. I guess my phrasing reveals my bias towards the "epistemic" part of this community rather than the "instrumental" side. My personal preference is to shift the community focus back towards epistemic rationality, but that is a separate discussion which I did not intend to raise here. The community should discuss this separately.

users may not repeatedly bring up the same controversial discussion outside of their original context

How could we track this, other than relying on mods to be like "ugh, this poster again"?

There would have to be some moderator discretion on this issue. My personal view is that we should err on the side of allowing most content. This language was intended for extreme cases where the community consensus is clear that a line has been crossed, such as Eugine, AdvancedAtheist or Jim Donald.

professionally edited rationality journal

Woah. Is this really a thing that MIRI could (resources permitting) just like ... do?

Yes, they can certainly do this if they have the resources. Initially, academics may not take the journal seriously and it definitely will not be indexed in academic databases. If the quality is sufficiently high, it is conceivable that this may change.