integer is a valid, partially-supported data type in our managed schema. The policy is bugged in that it fails to allow the integer data type. The UI is incomplete for the same reason. Given this information we have 2 choices:
A. Fix the policy and the UI to support integer properly
B. Deprecate integer and fix the CSV import problems caused by using number instead
Everyone was so surprised to learn that integer was a valid type and we've operated for so long thinking we had to use number that I'm inclined to go with B and address the problems with number in CSV import. That type doesn't seem to cause any problems anywhere else.