You just CAN'T spend freshly minted coins until there's 520 more blocks above the one you minted.
Yes. But exchanges and businesses could still wait until there's 1040, 2080 or 10400 before they take your fresh coins if they don't want the risk of transaction reversal.
We could make the standard wallet freeze coins for that much longer, so they can't be put in outgoing transactions. If someone receives "fresh" coins, they know the other person is going all the way to use a hacked wallet which immediately flags it as fishy.
Well, this hinders the usability of YAC, then... YAC would be absolutely unusable the way you propose.
With the workaround I proposed, you can be certain that only someone with control of 51% or more of the network hashrate can orphan blocks - and that it actually costs him something to attempt that kind of thing.
The way it is now even a McDonald's worker screaming for higher minimum wage can orphan as many YAC blocks as he likes.