When you join an ACO, you still have to submit for Promoting Interoperability, you do not have to submit for quality and Improvement activity. ACO will submit for quality.
That being said if you suspect ACO performance is not as great, you can still do CDS and have that be reported as part of your Improvement activities.
There is also the tough that you can still submit for all 3 measures and let CMS pick the best for you.
Finally CDS can be tailored to do many stuff including notifying practice when annual wellness visit is due.
That is my 2-cent.
Thanks
aramiz
Houston