It could never be just a patch.. K11 is a customized tantra system and I have to make Kx12 compatible with that.
Did you know what items are incompatible just yet? Even I dont know it..
Here how it will goes
The K11 items/chars will be migrated to Kx12 server
Players will download a new client.
K11 server will be taken offline, then after sometime make it dedicated to Kx12 Kruma or some map for less lag.
If an item like armors, weapons got problem then I will make something close to that to compensate.
But this will take time.