I am really hyped for this match, both coming from loses, both heavy hitters, both defeated by Joseph Parker. Both are money makers, WIlder being S tier "star" at that. So we can rule out any unknown contenders.
I like the fight as a stand-alone. Somebody is going to get knocked out. The winner might fight Joshua I think. Which would be kind of cheap.
Hrgovic is probably on hold regarding the fight for the title, and after the fight with Dubois, a rematch against Zhang would be perfectly fine...
It's a fight that makes sense for both... They're both overrated considering their records - Zhang is currently 2-2-1 against top 200 ranked fighters and Wilder has never beaten a legit contender. But both recognize the other is beatable and yet carries a reputation that could propel them into a position to get more attention... Either by earning them a cashout fight (Joshua?) or by rescuing their ability to sell in their own right. Losing this finishes whichever gets KO'd... Going to cards probably finishes both, nobody watches them for anything other than heavy punching (I'll be amazed if this does go the distance, though). I think Zhang would chase a big cash fight (Joshua), or a title fight with Hrgovic/Dubois as a last/only chance at ever holding a belt. I'm not sure what Wilder would do - I'm not sure he really wants Joshua, knowing he'd take a career ending beating... But he might go after someone who's declined but has reputation - Whyte or Joyce, maybe?
Hard to say whoever wins doesn't have much time left as they are both old. With Usyk/Fury rematch in October followed by the IBF mandatory which will be either Joshua or Hrgovic if they fight in Sept as touted, they are not getting a title shot next or a shot at Joshua or Hrgovic.