Proksa and his people must be supremely confident to take such a fight on short notice. His career has stalled for so long its time to put up or shut up. TBH I didn't like the Barker match because they co share the same promoter and the fight would happen in the UK, stacking the odds against Proksa. Even if Proksa losses to Golovkin, if he can manage to impress in the process, his stock and audience goes way up.
The more I think about this the more I think it will end early. If by some method Proksa has suddenly learned defense than he may be a threat but his low hands style make me fear GGG will ko him early. It's also confirmed now over at the scene.