If it works, it is definitely not a gimmick.
As somebody who is switching from SLR to mirrorless for the weight savings on backcountry excursions, weather sealing is huge. I've killed multiple canon lenses and one body (thankfully still under warranty) from rough treatment in the outdoors, and missed a lot of shots because I didn't want to pull my camera out of my bag in the rain.
My dream X Pro2 is weather sealed, has in-body stabilization, and backside illumination. That combination would be killer, for me; every shot I want to get but don't is because of wet weather or low light. A bigger sensor would be great, too, but it's not worth having a heavier or less-durable body for me. I'm looking at you, Sony.
