Adobe released Aperture Importer, their official Aperture to Lightroom conversion tool. It operates as a plug-in to Lightroom (v5.6 required). It appears that you point it at an Aperture Library and let it rip. There's no details on how the images are imported. One would assume the Aperture folder and project hierarchy are used to create the structure of the Lightroom catalog.

An interesting item is that stacks are imported, although done as keywords in Lightroom. I can understand color labels and faces as keywords. I'm not sure how keywording a stack works. I certainly hope Adobe produces more documentation on how their converter works... or maybe they are leaving that to "the internet" at large.

I haven't tried out Aperture Importer. With all of the book work I'm doing, I won't get to it for several weeks. I'm still patiently waiting to see what Photos will offer in OS X Yosemite (also released today) in the spring. There's certainly no harm in experimenting with the conversion tools in the meantime. In the meantime I, like you, will be watching the web and the experiences of others making their transitions away from Aperture.