I'm not sure Kincaid can qualify as a "dark horse" candidate. He's far and away the best TE in the league on a number of metrics, except the one that really matters...availability. If he's healthy he will be 1st team All Pro, Pro Bowl, etc. Total stud. The injuries are the concern.
That said, I'll pick 3 others:
--Coleman. He was great week 1 last year, then like vanished. Some of that has to do with McD's process-doghouse. If Coleman can figure out time management and show up on time, I see a breakout, esp. with Moore and hopefully Kincaid taking attention away from him.
--Dorian Williams. He is built for a 3-4, ran it in college, and is about to pop during a contract year.
--IGB/Hariston. I'm not sure either will "pop" others, but the tandem breaks out by foiling other teams. IBG and Hariston together allow the DC to play matchup against WRs as they both offer elite skillsets at what they do (speed for Hairston, man/press for IGB).