I know you like to group things, so, while I'll keep your list, I'd draw certain lines:
Serious contenders:
1. Federer
2. Murray
3. Nadal
4. Djokovic
Potential (but unlikely) winners (and I wouldn't necessarily agree with your order):
5. Raonic
6. Zverev
7. Kyrgios
8. Dimitrov
9. Cilic
10. Wawrinka
Dark horses/spoilers:
11. Del Potro
12. Nishikori
13. Tsonga
14. Berdych
15. Goffin
Very good way of putting things. My list would be very close to that, but I would really correct for the grass factor and current form, so it becomes:
Serious contenders:
1. Federer
2. Murray
Potential (but unlikely) winners:
3. Raonic (I know he has not done much lately, but he is the current runner up)
4. Djokovic (big question mark here, position due to historical results on grass)
5. Nadal (Nadal bellow the two players above as his results on grass have been simply too poor, in fact #5 is still generous, no matter how well he played on clay).
6. Cilic (let´s see how Cilic plays on grass pre-Wimbledon, I wont´t be surprised if he arrives in Wimbledon being considered a serious threat).
7. Wawrinka
Dark horses/spoilers:
Zverev, Kyrgios, Dimitrov, del Potro, Steve Johson, Tsonga, Isner
No particular order here, in fact I would put a huge question mark over Zverev. He could improve his net skills, and I can see him being eliminated in a quick match where he takes too long to make needed adjustments.
You all know I´m not on the Kyrgios bandwagon, but his game and attitude suits grass perfectly. I erased Nishikori, Berdych and Goffin, and added Steve Johnson (my "surprise" dark horse, very good serve, good all around game and good net skills) and Isner, who can never be discounted here due to his serve and is having decent results this year.
JMdP is practicing that slice back hand for a year and maybe this could help him on grass. He already had good runs on the surface before...
