I doubt they would do that, unless an individual creator preferred to release their stories as longer form graphic novels instead of monthly issues -- which, in theory would be conceivable since Image is all about giving creators the freedom to do what they want.  But I'm assuming payouts for their creator-owned series are tied to the monthly cycle, so unless a creator had another form of regular income (or they had enough money saved up to last them six months or so between releases), graphic novels would basically mean they are getting paid only a couple of times a year.  That might work for a writer, who can support himself with other monthly series work, but I doubt that would be feasible for an artist.

Image only does the lower priced trade for the first volume.  After that, it's the regular price.  So I don't think that it necessarily encourages people to trade wait, since the later volumes, while cheaper, are closer in price to buying single issues (and as I pointed out earlier, lack the backmatter content that many titles are including these days).  I think it's designed more to lower the barrier to entry for people who want to jump on to a series that's already started.  Image titles tend to generate a lot of buzz (and speculation) in the early issues, and sometimes that makes it hard for someone to try out or jump on to a series a couple of issues in if prices for #1 and #2 are going through the roof.  Also, unlike Marvel and DC, Image titles don't really do relaunches or reboots, and they usually have a built-in end point, so making the first trade inexpensive encourages people to try out a new series and stay on for the rest.  I think it's actually a pretty smart business strategy.