I am pretty sure (hope to be wrong) that the Mac Pro will be modular and not a tower. For a simple reason – this way you will only be able to buy 'extensions' from Apple.
The only thing that makes we worried on that, or doubt it a touch, is just that Apple seems to have shown that they aren't interested in selling key additional components beyond a few dongles.
So much of the USB-C frustration for an average user is that Apple hasn't taken it upon themselves to really build out a robust 1st part line of accessories that covers a lot of use cases. They have some, sure, but it's sort of feels like they did the bare minimum and then just are leaving it up to the rest of the tech world to fill in large gaps.
That, frankly, sucks for an Apple customer, who is used to and expects Apple to be the solution to the problems, thus at least part of the price premium they expect.
That LG monitor situation was another similar example. One that went so poorly, they are apparently back in the game of making at least one monitor right now - although I bet that's solely for the Mac Pro purposes.
Pretty odd from a company that liked to tout the full chain of MacBook Pro + Apple Thunderbolt Monitor as your docking solution at one point.