reTyre have launched a tire system with a zip which allows you to fit a skin over the base tire. This allows a road tire to be quickly converted into an off-road or a snow tire. The tire doesn’t need to be deflated and re-inflated to fit the skin, it is simply zipped over the tire.
This could be a neat solution for long distance adventure rides or for covering distance on the road before hitting the trail. However, with tires being such an important part of a bike it will need to be of the highest quality to tempt serious cyclists. The join is where the two ends of the skin meet is also a cause for some concern. Whether this creates a noticible bump or increase in rolling resistance is yet to be determined. The risk of the skin coming loose and jaming the wheel would also worry me.