I tried looking up his residence and found that he has a permanent residence in McLean, Virginia and another in Washington, DC. He did have a condo in the West Side of NYC, but sold it in 2016. So for legal purposes he probably would register his home state as Virginia, putting Allen out of contention. However as Clinton's example shows that doesn't prevent him from picking a Southerner as a running mate. There's Lamar Alexander of TN, Phil Gramm of TX, and Carroll Campbell of SC. That said Kemp would still be a good choice to appeal to fiscal and social conservatives, and in Powell's mind it could help to make inroads with the Democrats' northern base (that didn't work out for Dole but it might work for Powell).