I think this is my first post in this forum so let me please take this opportunity to say Hello to Everyone!
Back to the topic...
Dont know how it is done in DDM85 but in DDM60Pro (i.e. cabling through the mount) the hub, that sits in DEC head of the mount is linked directly to USB Hub socket on RA. That's to say, for the USB Hub purposes e.g. to connect USB 3.0 Camera, the inner electronics should not interfere as it does not go through "electronic board". Could be in DDM85 it's really the case...
In any case, I just wonder why would you need 3.0? Some time back it was also my "dream" but then I realized it's just "nice to have", rather than "must have".
For the mount control itself USB 2.0 should be sufficient (there is no massive data transfer) and the 3.0 could be achieved as per ChristerS's post. An alternative would be to use "data" socket (if not used of course) + custom cabling. There is a post on this solution somewhere here in the forum, will try to find it when back home tonight.
Obviously it requires a bit of "bricolage" as french speaker say, soldering, connectors etc. but just note:
(1) you need to play with cables anyway i.e. changing hub or inventing a small bit of new electronics
(2) you take a risk of breaking something that is working - ASA support team would not like this approach neither
Does it make sense?