6 of the Top 11 relievers in fWAR are FA to be, 3 of them are young enough to potentially get a 3+ year deal for serious money(Holmes, Hoffman, Strahm), and 3 of them are not(Jensen, Robertson, Yates). There's also a few guys who have been good closers who are not quite in that elite FIP grouping hitting FA(Scott, Estevez) so I think it's fair to say it should be a pretty robust market.
In addition to the FA market though, I wonder if we see a more modern twist on the Wade Davis deal, and see a trade for a reliever near FA. You give up some currency to do it but you also lose the multi-year downside that we've seen exists even with guys getting higher end reliever deals(hint: the Cubs just released one). Fairbanks, Kopech, Helsley, Kimbrel, and Iglesias are all names that would qualify, probably others that my 60 seconds of Fangraphs searching left behind.