any attempt at cashing out these coins will immediately reveal who it was
Nope. That's only true if every single exchange, ICO, etc that supports NEM is MANUALLY tracking the stolen XEM and manually blacklisting in real time which is simply not going to happen. Even if so, many exchanges don't require verification so it wouldn't reveal who attempted to cash out.
Even with the tagging system, chances are there will be some exchanges that won't utilize it.
Actually according to jeff in his interview , its a very easy process to see if any tagged coins enter their system. Its just a matter of adding some code to their api and its all done automatically.
I don't see why all exchanges wouldn't do it as they are opening up themselves to money laundering charges if they start selling stolen coins.
Hard fork seems to be a no no also which is good news.
Best bet for hacker is to seek a bounty and return the funds
NEM is in danger of falling off the map here. Team needs to do something big. Is catapult ever happening? Wasnt it supposed to be last August?