First of all, there appears to be a limit on how large an image Lightroom is willing to accept, which I am guessing is 10,000 pixels in any one dimension.. can anyone confirm this, or better yet tell me what the exact maximum pixel dimensions are?
So here's at least one answer for anyone else who's interested:
As I suspected, the limit is 10,000 pixels in any one dimension. Lightroom will not import an image with 10,001 pixels along one side.
10K is a nice round number, I suppose, but seems a touch arbitrary. Here's hoping they increase that, as there are lots of images in my collection I won't be able to work with via Lightroom if not..