What worries me is the unexpected gap in the management of key words. The use of Media Pro in direct comparison with Aperture has not become really clear to me.
I am now waiting for what is being proposed here.
Here's the thing. There's no rush. Aperture is a pretty good DAM, and will continue to work with 10.10 Yosemite. Aperture will be a workable professional tool for another year or more.
Not saying that this would work for your workflow, but what I've been doing is continuing to manage the files in Aperture (I prefer Aperture's import folder creation and dating, based around image date rather than import date), and then just do an import of the main directory into Capture One. It picks up any new files and folders, and then I do any image correction, cropping, etc in Capture One.
(Of course, I work with referenced images rather than managed, not sure that would work as well if you used managed images.)
Eventually if/when Capture One catches up the DAM features and keyword management they can be exported out of Aperture with XMP sidecar files, or alternatively, with Photos for OSX shows up next year that can be evaluated as a photo management solution (Aperture libraries will import with keywords, edits, etc intact) and decide then.
The way it's sounding, you'll be able to (for example) search for an image keyword via the OS in Spotlight.