This used to be somewhat common, before opensource really took off. I worked for 2 different companies in the late 90's early 00's that had everything in escrow as certain customers demanded it.
On the one hand it was a pain to work towards, as the requirements had little immediate value (new features needed lengthy documentation, lots of features had to be stripped out, long (manual) test checklists, etc) but on the other hand, it got you thinking about how to build software that would need to last longer than the company you're in. Made me realise that feature creep/bloat was what was holding the product back, not the Next Big Thing(tm).