Sketchup has only been mentioned a couple of times, but it is a big market.
For hardcore 3D artists like ourselves, Sketchup probably seems irrelevant, however the vast majority of architectural firms I have worked for use Sketchup.
The LARGEST architectural practice IN THE WORLD uses Sketchup as part of their standard line. Sketchup is simple to learn and easy to use, which is why many architects and designers use it. These people are pros in their fields, but 'amateurs' when it comes to 3d.
Corona is VERY easy to use, so would be a perfect match for Sketchup. From what I've seen, Sketchup is more and more the standard for architects/designers, so if there was a good plugin for Corona, at a reasonable price, I can easily see Corona becoming the standard renderer for architects/designers.
It's definitely a different market (and certainly a bid one), and if Corona was complicated and unwieldy I wouldn't recommend it BUT Corona is simple, easy to use and just looks great, so I think it would be a perfect fit.
Anyway Sketchup is my vote.