I think it is certain Mo will add to the pen by trades. With all the new additions to the system, he has to trade off some guys, and what else is he going to be going for?
Brian has pointed out several times that there are now more starter candidates than there are rotation slots in the upper levels, with more guys pushing up from below. This threatens to force some of them into reliever roles. So some guys will surely go. It seems like it will be multiples going for fewer returning, and those returning seem likely to be ained at improving the pen. At least that’s how it looks in my world. So I’m not looking for any big reliever splash in the FA market.