The XEM wallet at bittrex is on "Automated Maintenance".
How do other (your) exchanges handle it? I'm just curious.
Are there estimates how long they will have their wallets on maintenance?

Maintenance until they figure out what went wrong with coincheck. Makes sense. Or else they are scrambling to enable multisig which apparently coincheck didn't bother to.

Update :

NEM + Coincheck are working together to track + flag the hacked wallets + related accounts with the objective of tracing the ultimate owners of the suspected wallets. NEM is identifying + flagging suspected wallets holding the stolen funds + sending info to exchanges. More soon.

I don't think so, it's likely just a security measure.

Bittrex is still allowing trading for XEM already within the exchange, but the wallet is on automatic maintenance along with 5 other coins.

I guess this is a precautionary measure.

Of course, this is pure speculation until we hear the facts.

This things like this happens, now is the time to show our support buying more NEM 

Well as far as I understand there is not officially confirmed it's just rumors, in the worst case scenario is like @fragout said Nem will have to burn some coins but
At the end you will not loose your investment 

There aren't many XEM exchanges. All of them will have contacts with the NEM foundation. They would've needed to be to create their back end stuff. A few messages will lock the hacker out of all exchanges.

So how was this exchange hacked? And why were all coins on one SINGLE Wallet? Does that mean every Wallet could also be hacked only because they have no multi-signature on? That would not be good.

700k coins will do that to you. I really believe/believed in this one and all this is rather depressing. I’m of the belief that reputation/marketing are of huge importance and this just doesn’t help.