Traveling to Gimmelwald for a two night stay and my daughter has a medium size suitcase that we would rather not haul up and down in trams etc. I see that Interlaken Ost has both lockers and a luggage storage counter. The question that I cannot find in my internet searches is: How long can I leave a bag at the station? Is two days acceptable?
If you can carry it as far as Interlaken Ost then I don't see any reason you can't continue with it until Gimmelwald. I mean, you roll it across the street from the train to the gondola - it's not like you'll be hoisting it on your back, right? I think it will be more work storing and retrieving it than it would be just to take it with you.
Lockers in Zurich are available for up to 72 hours and I would expect them to be consistent in their policy across stations. Luggage deposit offices are almost always very flexible on length of deposit.