Locking cards for mining would likely have repercussions elsewhere, as the calls and calculations used are also likely used in gaming and other applications like deep learning. It'd also slow down sales for Nvidia, even though mining profits aren't too good as of right now.

Last time mining cards were released from Nvidia, sales likely weren't good, and the cards were much harder to obtain than regular cards anyways, as well as more expensive AFAIK. They may not be going with that route this time around.