I disagree that GitHub's project pages "suck for SEO". GitHub's pages rank quite highly on Google. A search for "cancan" for example returns my project as the first result. A search for "homebrew" returns GitHub's page as the 3rd result and the custom project page as the 4th result.

Also, creating a separate page for a project means there will no longer be one page for people to link to. Links will be split across the two pages, and links are important for SEO.

I agree a separate project page is great for branding and makes it look like a dedicated, serious project; but I wouldn't do it for SEO purposes.

Otherwise thanks for the great list of ideas.