But, ostensibly, there's going to be thunderbolt devices soon which, while having a USB Type-C plug, won't work in a regular USB port despite the Type-C plug.
Given that USB 3.1 + Type C ports support USB PD (100 Watts), and 10 Gigabit signaling rate (7.1 Gigabits demonstrated transmit) - the need for thunderbolt devices will be so excessively rare for the average consumer as to be a non-issue.
For the few Pro Users who Specifically paid a small fortune for their thunderbolt device - they will certainly know which port to plug it into, there will be zero confusion.
What's nice (awesome) about this, though, is that when Apple/Microsoft/Sony/Asus/whoever decides to differentiate their high-end products by offering Thunderbolt 3 ports that people will rarely have a use for, they can actually make use of them immediately as USB 3.1 ports. Right now I have a MacBook Air w/2 USB + 1 Thunderbolt Port. I have too carry Ethernet Dongles for both Thunderbolt and USB to cover the situation in which I run out of ports and need ethernet. And I frequently run into a situation in which I've used up my two USB ports, and my third adapter isn't thunderbolt (I know, I should carry a Thunderbolt -> USB adapter, but god, I carry so many cables already).
In this new world - I would have three, fully functional USB ports, with one of them also capable of functioning as a thunderbolt port should I have a Thunderbolt peripheral.
Source? Sure, it's theoretically possible that a TB3 5K@60Hz monitor won't work when plugged into a USB Type C port. But there would be no good reason for that, it should downgrade smoothly to either 5K@30Hz or 4K@60Hz.
I'm running off of the assumption that Thunderbolt continues to use a different physical layer (which it pretty much has to to go faster than USB 3.1), and is piggy backing on USB Type-C's "Alternate Mode" which lets you negotiate different physical layers that you have a transceiver for.
Sure, but why wouldn't the TB3 transceivers be designed to support USB 3.1 as well? Those transceivers have a wide range of dynamic adaptation to support high speed transmission, so it doesn't seem like much of a stretch to adapt to USB 3.1 signalling levels & protocol.
Because even above the physical layer, the two protocols are very, very different to the point that you're nearly doubling the amount of work that you have to do. USB at it's core is a host polled interface that looks like a network, and Thunderbolt is at it's core a multimaster RDMA interface. You'd basically be designing two different devices.
For the few Pro Users who Specifically paid a small fortune for their thunderbolt device - they will certainly know which port to plug it into, there will be zero confusion.
What's nice (awesome) about this, though, is that when Apple/Microsoft/Sony/Asus/whoever decides to differentiate their high-end products by offering Thunderbolt 3 ports that people will rarely have a use for, they can actually make use of them immediately as USB 3.1 ports. Right now I have a MacBook Air w/2 USB + 1 Thunderbolt Port. I have too carry Ethernet Dongles for both Thunderbolt and USB to cover the situation in which I run out of ports and need ethernet. And I frequently run into a situation in which I've used up my two USB ports, and my third adapter isn't thunderbolt (I know, I should carry a Thunderbolt -> USB adapter, but god, I carry so many cables already).
In this new world - I would have three, fully functional USB ports, with one of them also capable of functioning as a thunderbolt port should I have a Thunderbolt peripheral.
Awesomeness.