Archiving PPro projects for professional shop possible?

Our shop outputs about 300 high-end deliverables a year. We run a mission critical operation with full offsite backups to tape etc. Our clients (some very high profile) frequently come back after several years in some cases to revise past works. We are using Media composer currently but am curious about using Premier on a few projects. Everyone I talk to is NOT confident that Adobe will provide support for this level of professional archive workflow. I was told they have a history of arbitrarily discontinuing older versions and have even sued creatives from opening discontinued versions because its considered "rental software" and Adobe will say when and who can rent a certain license. Does Adobe guarantee functionality in future updates like Avid does or are all past works simply at the whim of Adobe? Is there a set date Adobe pulls a specific version software license professionals can plan for? Someone did mention it may be possible to regularly open every single project, link everything back up and resave it as new versions come out but its obvious that would be just ridiculous and a total mess.