Sorry for a very late reply, I must have missed this thread.
The limitations were indeed set for technical reasons. It is already quite difficult to make sure that each aspect ratio and image size blends into the overall site design without creating problems. We already pushed the limits when allowing 2048 px photos.
Ultra-wide panoramas can be very nice, but they would look awkward on the homepage. We explicitly did not want to force or restrict any aspect ratios, but also have no technical solution to support exceptions to our min/max limits. Thus, 2048x600 px is the widest we can handle for the time being.
None are more hopelessly enslaved than those who falsely believe they are free.
(Johann Wolfgang von Goethe)