Hello anticomformist,
It depends on what you mean with "offline/cold wallet masternode". A masternode seeds the blockchain, validates transactions and blocks roughly speaking.
These are both things that require the node to be connected to the internet. In case you are referring to cold staking of coins, there are a few coins that have presented ways of achieving this.
The following article on medium explains the different kinds of solutions developers have come up with to enable the cold staking of coins (
here).
In the future we might see more coins having implemented the means to facilitate cold staking.
With kind regards,
The Anycoin Direct team