Right now, there are something like 2900 UM system prompts. It's not supported to change them, and installing a CU overwrites them. It would be nice to have it supported to change them, along with a list of which prompts contain which message.
Right now, when you disable someone from UM, it leaves the EUM addresses assigned to the user. It would be nice to see a prompt asking if you'd like those removed. Otherwise you have to manually remove them to make that extension available for another user.
I'd like to see the Cortana interface folded into the next version of UM. The natural speech and digital assistance would put UM light years ahead of other platforms. Seems like low hanging fruit for the next version.