I started a new thread to discuss some design sketches that show my original plans for Cecily in TiddlyWiki 5:
But to answer your question more directly, one thing that has changed since I did the original Cecily prototype in 2008 is that there have been a string of commercial and open source products that embody that central idea of an infinite 2D canvas onto which one can slide resizable panels, with pan-and-zoom as the primary navigation metaphor.
Most famously, there was Presi. Now one of the most interesting examples that I know of is Muse, an iPad app:
So, one good thing is that I have had the opportunity to play around with some very polished and sophisticated implementations of the basic idea. Iāve found that the original metaphor that I was attracted to is actually not sufficient to make a functional user interface. Thereās too much scrolling and squinting, and the UI affordances donāt help with obvious use cases (āarrange all the tiddlers tagged foobar in a squareā). Zoomable user interfaces have always been primarily concerned with navigation.
Itās still an area I think about a lot, but havenāt got to the point where implementation work has risen to the top of my stack.