The idea of Sherlock x POI is just AWWWWWWWWWESOME! I can't help but come up with several silly thoughts...
1. Characters in POI have plenty of secrets, and Sherlock, by all means, is damn good at exposing them.
2. JOHNs!
3. Two former military Johns. Might have connection or might not. Anyway it must be a lot of fun to put them together and make friends, XD
4. After S2E3 Sherlock is a "Dead man", too. That makes three of them. Must have so much to chat about. Let alone "keep away from the person they love".
5. "Big Brother" vs "The Machine"
6. Sherlock being watched...even when he is an OCEAN away from Mycroft! That must be most annoyi