Creo Mechanism: reciprocating rack and pinion

I think this is possible. If you have not used mechanism before it may be tricky to get it working. Getting the two mechanisms to hand off to each other at the motion reversal will likely not be intuitive. You will probably have to impose some logic on the servo motors to reverse the direction.

One of the mechanism SMEs should weigh in on this with some practical suggestions.

Yes, this can be done. You will need to pay very close attention to the details of the geometry so that you do not have either both rack segments being driven at the same time. You can do this with 1 liftoff cam pair if you create your geometry properly with a "handoff gap". It also may work best as a "dynamic" analysis to aid in making sure there is separation between the first gear engagement and the next. I hope this makes sense without any graphical assistance.