Personally, I feel that third-party development on Mint has remained strong. There are Peppers for the most common statistics tracking needs (some statistics even have multiple Peppers), and Mint customers seem to embrace the add-ons. It’s rare for paid software to have such an active development community.
I can see where you’re coming from though. There are some rare / custom statistics that people want, that not everyone wants. You’re hoping that by offering free Mint licenses some of those Peppers will be developed.
Being a Pepper developer, I can say that I doubt free licenses would have that effect. I guarantee you all Pepper developers bought Mint and then found they needed some functionality which Mint did not offer. I know all of the Peppers I have developed have come out of a personal need. Instead of doing all of that work for myself, I decided it would be best to share my work with others. Now, not every Pepper developer may feel that way, but I’m pretty confident that’s how most developers operate. They’ve already bought Mint and are just sharing their work with others.
If people are looking for custom Peppers, I believe the best way is to personally hire a Pepper developer to develop the Pepper. Most Pepper developers are in the web development industry doing freelance and would be happy to code for a paycheck. I know I’ve seen this done in the past on the Mint forums.
So to sum things up, I feel most of the Peppers which everyone benefits have either been developed already or will be developed if enough people express a need. If there is a custom Pepper that someone needs, the best way to get it developed is to hire a Pepper developer.