Here's the problem with the exchange theory.
These wallets show a very consistent growth in iXcoins.
An exchange would see wild fluctuations as people sell, transfer and withdraw large amounts. Like I pulled out 500,000 IXC in just 1 day and I did the same from vircurex when I moved to Cryptsy.
If it was the ixcoin cold wallet for an exchange you wouldn't see constant withdrawals. With a large number of peope merge mining to their exchange address this would create a surplus in the hot wallet which would periodically be sent to the cold wallet in large chunks.