#4. A transitional WWE title run for The Miz

It's possible that coupled along with the previous reason, The Miz could simply be in for a transitional WWE title run. While making Drew McIntyre a three-time WWE Champion in nine months is less than ideal, it could be done by having Keith Lee pinned in their title match on RAW next week.
It could simply be a 'Thank you for your years of service' run for The Miz - similar to the World Championship run Mark Henry had in 2011 in his 'Hall of Pain' run.
Top WWE star punished? More details HERE
#3. To have Drew McIntyre legitimately destroy The Miz

The Miz regaining the MITB briefcase could be WWE's way of further strengthening Drew McIntyre. It could be in a scenario where Drew McIntyre has already retained the WWE Championship, after which The Miz would attempt to cash-in at the most opportune moment.
A clean victory for Drew McIntyre would undoubtedly hurt The Miz, but from WWE's perspective, The A-Lister is likely far past his prime, while McIntyre is just at the start of his.