While I don't like the new CC model, which version of ID ever allowed opening its files in a previous version natively?
No one is forcing me to sign-up to CC. Not one previous customer has indicated they are moving forward with CC. Heck, most of my ID customers are using 5.5, maybe a third are using CS6. Should I get a new customer requiring CC, I'll pay for the use of it and drop it when the deliverables have been handed over. I don't like that this is how I will need to handle it, but I'll cross those roads as I come to them.
Adobe is under no obligation to make my life easy in the use/licensing of their software. Just like I get to make decisions that better my businesses in my POV, they do too. We both get to deal with the fall-out for those decisions.
Take care, Mike
You do have a choice: stop using Adobe products. I switched to other products eight months ago, because I expected Adobe to go down this road sooner or later. And I have been a loyal Adobe user since Photoshop 3!
Many alternatives for InDesign out there.
When enough users stop using Adobe products, the market will balance out. You are in control - Adobe tries very hard to convince their users that they do not have any other choice, but to go along with the CC model. Obviously that is not true, and viable alternatives exist (well, except for After Effects).