During a recent stream from NetherRealm Studios Twitch channel had Tyler Lansdown (Community Manager) and Derek Kirtzic (Senior Systems Designer) attend some of the concerns that people have been posting online. Specifically, they wanted to talk about what you can and cannot buy in their store, as well as the Krypt boxes issue.
Source: N4G PC NetherRealm Explains Microtransactions and Unlockables