Plugin-based software marketing scheme

I'm in the planning stages of a rather large project (think Photoshop killer) that will be released to the public at large. Most of the features are plugable and I plan to release the plugin sdk for free. I'll also be trying to garner a bit of a community of third-party plugin developers.

I'm thinking of releasing two versions of the program:

XYZ Lite, a freeware downloadable version and
XYZ Pro, a commercial version to be sold online and (hopefully) in stores.

Both are full featured, however:

Lite will only run plugins which are signed by the company while pro will run any plugin, signed or not. As a plugin developer, you could choose to sign your plugin for a reasonable fee.

I'm thinking that the free version would run unsigned plugins created on the same machine so developers would not be forced to buy the program.

I've not delved into the implementation of this system and I'm using the term 'signed' in place of 'approved', but you get the picture.

Is this a good idea?