you forgot an important player in this list, donskoy...where would he slot in? i consider him a master manipulator using mind-control to make federer beat himself...Fit (and focused) Djokovic is the biggest threat to Fed, obviously (BTW, Federer is also the biggest threat to Djokovic and was the only one who could challenge him in his dominant run, along with beast-mode Wawrinka).
Nadal and Del Potro come next.
Then, Murray, Wawrinka and in-form big hitters like Raonic, Cilic etc.
Then finally Tsonga, Dimitrov, Berdych, Nishikori etc.
That's how I see it.
also i don't know what your basis is for putting delpo so high up...threat for me means federer at his best can be beaten by these players...for me that shortens the list considerably...
djokovic at his best is capable of doing it, so obviously is nadal and murray (at his absolute best) as well, pre-injury delpo did it in the u.s open final and was capable (i doubt it now though)...stan has the talent but he is at a psychological disadvantage against him for multiple reasons..but the rest don't really stand much of a chance against him at or near his best...
the thing is he has not been close to his best all that often in recent years and that kind of provides an opening for a lot of players, an even wider list than what you mentioned...