I don't see that approach working in any competitive product marketplace. This is the kind of candy you don't want to throw to you competitor.

Anecdotal, there's a company that built their core product on Symfony 0.9x, and never upgraded. That was started around 6 years ago. The company is now worth 1+ billion on nasdaq, and still relies on Symfony 0.9x for the core functionality.

From a development point of view it sucks. Ask any developers.

From the business point of view, staying away from the kind of 6 month no feature s-bugs-only period you're talking about, is probably the reason it could beat its main competitor, and succeed the way it did.