My suggestion goes entirely in the opposite direction than Redesign of tiddlywiki.com - TAKE 1
I'm no fan of a TiddlyWiki instance that serves all purposes for all people. Landing page, online demo, online documentation, and community test bed. When something tries to be all things for all people, it doesn't do all that great at any of the things. It is bloated and heavy (lethargic), and hard to navigate.
What I'm suggesting here is a proper portal, that does only that job: be a portal. A portal to all things, including many TiddlyWiki instances, each TiddlyWiki instance doing an intended job. Many online demos focused on what they are demoing. Many for online documentation. All of them available as community test beds. Any one TiddlyWiki instance able to behave as a client and/or a server to any other one.
ASIDE: Many TiddlyWiki instances for online documentation? YES! For example: a TiddlyWiki instance with the sole purpose of navigating and learning TiddlyWiki interface elements. That lets a visitor interact with it in the same way as the tutorial for TreeSheets (download TreeSheets and when you open it, you have access to the tutorial that invites you to try this and try that.)
Something like that. I'm never done piecing together what I'm thinking ...