Well, first, I applaud any efforts to improve/disrupt/whatever the rental market in this town, which is just comically awful. This sounds like it'd be exactly the kind of thing I wanted the last time I was looking, but ended up having to give up on at the time.
But - I don't actually see a solution there. You've got a very apt description of the problem and of what the solution would look like, but I do think there's a big leap from identifying those to actually going to something that works. The critical point to get past is of course actually having a number of interesting properties listed on your site, which requires overcoming the awkward network effects inherent in that market which the real estate agents obviously have a massive interest in perpetuating.
But don't let me get you down - I'm a bit cynical about this after my last experience flathunting, but everyone I speak to hates the system at the moment and would love something better. There are a ridiculous number of real estate agents in this town which implies there must be an awful lot of money in the market - ample room for someone to seriously undercut them while offering everyone involved a better deal.
Best of luck!