I'm afraid this is a highly speculative question, but I wanted to put it out and see if anyone can provide more insight.
Let's say that at some time in the future, during a Falcon 9 launch, but before stage separation, an anomaly is detected with the second stage that is going to cause a loss of mission. Theoretically, could the Falcon abort the assent and proceed to land with the second stage and payload still attached?
The extra weight might even help the landing. It would provide a more manageable T/W ratio and allow the F9 to avoid the tricky hover-slam landing. Of course the higher centre of mass isn't going to help things, and the landing software would need completely rewriting and new flight profile would need to be created.
TL;DR: Are the any engineering problems that would completely rule out a Falcon 9 aborting an assent and landing with its payload?