This will gut the local courier market, I think. Customer could simply enter pieces, weight, dimensions. A vehicle of sufficient capacity would be located and vectored to the customer. As a customer, you wouldn't be able to demand IMMEDIATE pickup, any more than an Uber "taxi" customer can. But if you need a couple of boxes taken across town same-day this would probably get it done.
What if you're a supplier in some little town who missed the window to get stuff on a truck and need 1700# of parts (2 skids) taken to an assembly plant 2.5 hours away NOW? Uber probably can't fill that need. They'd have to have a driver "on the clock" with a large enough vehicle to handle that load. Somebody who is willing to drive 150 miles or more as well. We're a strange lot -- equipped with bunks in the vehicle and comfortable sleeping at a strange Wal-Mart or truck stop. You ask your average person in Findlay, OH to go up to Sterling Heights Assembly (through Detroit) and they're not necessarily going to be comfortable with that. They might actually turn down your emergency load; just as the passenger-carriers can turn down requests.
Of course, if Uber hired on a guy with some 15 yo rust-bucket old Ford van... Chrysler might not like that either.