I see the use case but I guess I personally would arrange my different product versions in different namespaces like this:
productA:version1.0
productA:version1.1
productB:version1.0
productB:version1.1
Your approach looks nice to me because it is simple but what if the documentation is not linear?
E.g. productA:version1.1 is the current version but you need to change the documentation for productA:version1.0? Maybe this is not required in your case but in general it could occur.
Of course keeping a namespace per version is a lot of work. Not sure if there is a tool which can clone/copy the pages of a namespace into another. That means if you create a new version just copy the old version namespace to the new, e.g. copy productA:version1.1 to productA:version1.2.
Also, other people might prefer your solution, this is just some brainstorming.