I don't really see that there is much different between these portable devices and laptops, so I don't see that there are many issues. They are both computers and encryption and locking down should not be an issue. If it is not possible to to it now, then in the near future these things will be demanded and implemented.
I'm thinking a little earlier than you as far as PCs. I remember typing into my PC off of printouts so I could use a PC to work out something and then using a printer to send the results back so they could be hand entered into the mainframe again, plain stupidity. Could I get the guys who ran the mainframe to provide me with a CSV file. No way that's a security issue. Could I send the data back as a CSV, no way, you can't do that, the data needs to be send on the appropriate form. Two years later all the data was available and loadable with tab delimited files using kermit. Now days you just tap straight into a SQL server to generate whatever reports you require, in whatever format you want.
It may be that these new devices are storing and using a remote system and all the device is being used for is as a client, but somehow they will have to be integrated into our present IT systems, because that will be the way things will work.
You could see a person in a store ordering stuff on a tablet, expecting to see what is available and being able to get order it online. Just as you'd expect someone in the field to be able to work on a report and have the pictures/data available for a colleague back in the office, I don't know if these devices would be laptops or even tablet or phone devices. They could as easily be cameras, meters, or GPS devices.
I'm surprised at the vitriol that this topic has produced. I have always assumed it was a given that these devices would end up attached to a network, and the administrators that run these networks will have to work out how they will secure the network to accommodate these devices. If not an enterprise should easily still be stuck with mainframes teletypes and card readers, because clearly there is no security issue with these.