I'd like to see them pull another 10.6.
Just take a full update to do nothing but fix bugs, clean up code, do optimizations and refinements. Spend time tweaking and perfecting the already included tools. Not add anything that would take a very minimum amount of work to do. Just focus on the core OS itself and what's already included.
To be frank I'd really like to see MS do the exact same. Take a few update cycles to do NOTHING but fixing open bugs, cleaning up any code that needs it and spending time to re-write what needs to be. Just do what they can for 6mo-12mo focusing ONLY on bugs and performance. Don't add anything new. Just all hands-on deck to FIX.