This question is based on a few premises. It is now mid-season. Kelly Olynyk has satisfied you that he can play at least a tolerable level of defense in the NBA and will be best suited to playing as a stretch four. Jared Sullinger has shown no signs of being negatively affected by his back. The Pistons have determined that playing Drummond and Monroe on the floor is a bad idea because of floor spacing and are looking to deal one for a player who is a better fit.
In this scenario, the Celtics have two young power forwards who look like they can be above-average starters at the position (let's say it feels like a 50-50 case of who you think will be better, but both seem good to you), while the Pistons have two young centers.
If Detroit came around asking if the Celtics would like to do a deal so each team has a young power forward and a young center as their frontcourt of the future, would you be interested in a deal? Would you ask for a draft pick? Would you be willing to give one up?