A small thing, I know, but the progress indicator is highly disproportionate for a "typical" render with lots of white-space or backplate. This is obviously due to the renderer starting in the middle and working outwards. So when the progress indicator reaches 16%, the whole job is typically halfway there in terms of elapsed time. Here's a graph of a typical rate of progress for one such job.
It's not the biggest problem, I'll admit, but I wonder if the realtime renderer could quickly calculate a "centre-weighting factor" or similar so it recalibrates the progress indicator to be something more proportionate?