Yeah, PT did this before Sonar. BUT there are some major differences in the model!
If PT users don't pay for the upgrade by the end of the year... then the only way they can get any further updates is by purchasing the retail version AGAIN at full price! The guys that have the HD systems... they have to pay $599 a year to subscribe for updates. If they don't upgrade before the year is up then the only way they could have updates for their HD system is by purchasing A NEW HD system... because Pro Tools doesn't allow you to purchase HD software without buying the hardware.
Does anyone here know what Sonar's policy is if there is a lag in your subscription? IE at what point will you not be able to "upgrade" and instead have to purchase a new version at full price?