If they want to get new users and protect the old, what they could do is offer the BASIC version of sonar as a sub model, and producer version as a traditional purchase. The sub model would be like a pay to play demo. Better than a demo because you can keep using it over 30 days and it won't be crippled.
This would make it real easy for new people to try it out but would provide an avenue for traditional buyers, people who are comitted to the program. If I could try cubase for $10/month I would. I have loaded most of the available demos and between being crippled and the fact that if I want to keep working in them it requires a cash outlay, they are not enticing.
They could also provide incentive for people to buy producer and offer discounts for people who have paid into subscriptions.
At first I thought sub sounded like a scary departure, but as long as they continue to provide traditional sales version, it could work out. I wouldnt want someone "renting" the producer version however.
I think the rent model would benefit a company whose software is better than their market share.