It's a little unfair to think of any app as being isolated in terms of updates.
Even though Gallery hasn't had a 'tear down' style revamp for 2 years, it doesn't mean that it's not received any updates. Simply by being part of the Invision Community ecosystem, it receives all the updates that the core gets, including UI updates, notification updates, performance updates, etc.
Quite simply we do not feel that Gallery needs a major re-invention at this time.