Currently use QC to make custom layers for Bonix TV - a vision mixing kind of application for OS X with a kind of QC stack of layers, each layer being a composition with published ports and some protocols for data types. Also generate sports graphics and twitter feeds and so on for video score boards at large sporting venues.
Spent a few years learning Quartz Composer as my way back into coding from a decade away doing design related work. Film, graphics, studied Architecture for a few years and got involved in publishing then film. Now moving into front side web development. Hope to get into app dev with Vuo and rapid app prototyping.
You can get around this to some extent having an AppleScript file run outside of Vuo and pass the info by writing info to a text file, .info file or perhaps using OSC if you can find an Applescript way to write to OSC (I've never googled that option, text file is fine for my needs). Given that Vuo can export screensavers now, a few iTunes peak and poke nodes could be worthwhile, at least to pull track and playlist data.
I recall there was some QC Core Image filter code in one of their example comps to do this.
Vuo doesn't have CI filters, so I guess converting from the QC CI round-corners patch (if somebody can find it, it's not in the patch library) to ISL shader code for a Vuo node is one way you could get this done quickly if you can code GLSL. I forget how the code went, but was pretty straight forward maths using a comparison operator with the radius input to knock pixels on the corners out to (r,g,b,a,) = (0,0,0,0).