Who is left for the Klitschkos to beat?

I agree, but they're just a part of today's sport unfortunately.

If wlad is made to fight him, he has no choice really.

 

The sad fact: there is no real opposition

 

for Wlad:

from america-
arreola (in shape arreola will at least be a fun bloodbath while it last)
solis (olympian, skilled and worthy of a shot provided he gets in shape)
mitchell (atheletic and should be a decent "filler/mandatory" oppenent)
wilder (in 2-3 years exciting fight. can punch and is bigger than wlad)
thompson (mandatory. hopefully last meaningless one!)

from europe-
fury (likes to brawl and is improving. bigger than wlad. exciting to watch)
price (bigger than wlad. might be decent in 1-2 years)
povetkin (motivated povetkin could be like the solis of europe. olympian)
helenius (punches chance. good mandatory defence)
chisora (if he wins a couple more fights will be entertaining while it lasts)

10 opponents split across both markets. 4 out of ten have longer reach than wladimir with 3 of them being taller. so in wladimir's final years as champ we might see some genuine challenge purely based on styles.
of course wlad might retire after a few more fights, but I wont be surprised if he tries to nail most on this list because that would really cement his legacy. especially facing younger guys, some of which are bigger than him.

for vitali he really should just have 1 more fight and retire, preferably on a ko win. he won rather comfortably last time out, but he showed his age. I don't want to see the fearsome fighter turn into a point scoring olympian just because he wants to conserve stamina and stretch out his career!