So many things are on the table for Reyes this season. They've discussed a lot of options, and they want to take cues from his health and strength and performance this spring to determine the course they'll take. Yes, need will also factor into it. There are many outcomes for Reyes when opening day arrives:
-- He could be in the bullpen.
-- He could be in the rotation.
-- He could be a hybrid, pitching in both relief and starting roles.
-- He could be starting for Class AAA Memphis.
-- He could remain in extended spring training.
All of these are possible and the likelihood fluctuates but all hinges on his health, strength, and performance. (Say it with me now.) A piggyback is one possibility, sure. One drawback there is the Cardinals would have two pitchers who would not be available for consecutive days coming out of that day, and they would have to adjust their pitching plans accordingly or exercise a lot of roster manipulation. Reyes could certainly be a part of that. He'll have options to move back and forth, and that could give the Cardinals the ability to rest him for a stretch without the DL being in play. They haven't even ruled out the idea of him being the closer at some point this coming season.
What the Cardinals are banking on with Reyes and other relievers, like Miller, is that they have a manager and a pitching coach now nimble enough to use relievers and pitchers in a variety of ways to win games and not exhaust one group or come undone when a pitcher like Reyes is handsoff for his health.