Changelog 5.15:
*) added support for usb forwarding over tcp;
I don’t see such an option anywhere. What is this and how is it used?
Yea I was wondering the same thing.
Big mystery this is…
A guess, USB over IP. Allowing us to extend the usb port on a routerboard to a remote location. Useful for extending things like usb weather stations and web cams.
Maybe Mikrotik can confirm this and stop the speculation 
ANSWER:
You can attach USB device to RouterBOARD USB port and operate it by Windows computer.
However, this option is added to v6.x only, changelog entry was added by mistake, this option applies for v6.x
so HOW to do it.. in ip - usb is all grey..
It hasn’t been added to winbox yet.
Use terminal /ip usb
This was mistakenly added to changelog of v5.15, it actually was added in v6. It will not work in v5.15
There is an issue with usb over tcp, it does not function at 6.0beta2 properly. It will be fixed in the next beta version.
how is this working? is it possible to get TCP stream to computer, and access a USB device? Or is this just a tcp stream possible using beween two mikrotik routers. Is there some software, description what so ever about this function?
Agree, please give us some documentation on this new feature!
We are preparing documentation for usb forwarding over tcp, it should be ready very soon. As soon as it will be ready, link will be posted here.
still not ready?
It will be in v6.
v6 is not finished yet.
Is the documentation ready? “very soon” was over 6 months ago.
Is this what you were talking about?
http://forum.mikrotik.com/t/routeros-v6-release-candidate-1/59786/3
It might be the same thing, but the term “USB sharing” is not really accurate. It’s usb over tcp/ip (to make a really long virtual usb cable).
But, yes, it is probably the same thing.
USB forwarding was not working well, so we have removed that feature for now. We will research how to make it work better .
+1 for this. The usb forward is a really nice feature. Espesially to connec to to UPS. (MT have poor support for ups over usb, like “restart command”) There is also a need for this, as the serial port is gone to new MT devices. Earlier, the install engineer always had a loooooong serial cable, to connect two MT devices together if there was a problem in a tower. Nowdays, its not that easy, to connect the same way via USB. if we had a usb over ethernet, it would be “possible” or easier, to do stuff from remote. 
It is also a lot of other really nice features, and handy stuff to do with a feature like this.
any news?