one thing you might like to look into is having it talk with some of the todo websites out there, like remember the milk (one of the more popular ones)
The desktop app is free and it always will be. I'm even intending to open source it one day once the code is solid.
The business model is to provide added value via web-services. Some of it may also be free and some may be charged for.
So, being said that, It makes sense to provide migration path from RTM and alike, but integrating directly with it - not so much.