Nishikori flatters to deceive. Fast becoming more overrated than Sharapova was when she won Wimbledon by beating Serena. I'd like to see Goffin, Dmitrov, Kygrios win one. Not happening anytime soon but you can always hope.
Tsonga would also be nice, I love that gentle giant, unfortunately he reminds me too much of pre-2013 Wawrinka mentality-wise. Peak level is good enough to take out the top guys but can't sustain it long enough.
I doubt any one of them will win a slam any time soon. Maybe Berdych if his gf dumps him or Raonic. Maaaybe Tsonga. Coric is most likely, but I don't care if he wins to answer literally the question posed. I don't think Nishi is quite good enough unless he hits a Cilic or something weird again.