Concern is what. To do with the other places the water can come in. It took my 85L out in the rain once and it rained right through the focus distance window, the mount was dry between camera and back if the lens.
That's the exact problem with stuff like the dust donut - it can only attempt to fix the leak at the lens/body join and does nothing to seal up the rest of the holes in the lens. However, the 24-70 mk I is a weather sealed lens, so all those other potential water ingress points should be covered. Presuming yours only has damage to the rubber gasket at the lens mount, it should work - but as to whether its anywhere near as good as the genuine $211 Canon seal, I couldn't say. And I guess there will be a bit of a wait seeing as it's still at the kickstarter stage.
For now I think I'll just use the 50L for the rainy days . Perhaps even remove the seal as it is pretty chewed up.