Yeah I think leather will probably be fine. Kydex could be a problem. We know from experience that our heat treat will cause some significant changes to the blade shape, which we're going to account for, but its impossible to say for certain what kind of range we're looking at until they're done.
The K18 moved some, but being a double edged design (somewhat symmetrical the movement was somewhat canceled out), but the rapid quench of our Delta protocol will cause the spine and the edge to go through their transitions at different times and our blade shape will change some as a result. This is called sori and it has been an issue for a loooong time. We have a general idea of the amount (this is not our first rodeo) but it is an imperfect science and there will be a range.