I think the big problem, other than poor taste, is maintenance costs.
I mean, sure, the first dredge is easy. But then what?
Do you monitor new links in real time, or periodically? How do you check against previous payment?
Do you charge by domain, sub-domain, or page? Do variables count as separate pages for charging purposes?
Then there is publishing your IBL policy. As soon as your policy is known, you will attract less new links, severely challenging your revenue stream.
It's a bit like auctioning bits of the EM spectrum. Good for a fast buck, lousy for actual revenue. Ultimately, I think you need to either charge more, or make it an annual fee.
I'd probably go for the annual fee, with different payment plans (Per-link, multi-link blocks, and free interlinking, for example).
No reason it couldn't work for a very small number of websites, with very specific characteristics (high PR, name recognition, unique resources, independent traffic sources). Google has proved that such sites need not fear the ill will of the webmaster community, and you're not nearly as hated as them.