Is it worth waiting for Thunderbolt 3/USB C? Why? / Why not?
The usual advice: if you need a new computer now, buy now, if you're just craving that "new computer" smell and want the latest bleeding edge tech, wait as long as you can bear.
The problem with Thunderbolt 3/USB-C is that its anybody's guess whether either or both of these are going to take off, and if so, how quickly and completely. So far, there are a couple of recently announced (not shipping yet AFAIK) Dell laptops and one full-size
Gigabyte motherboard with Thunderbolt 3 ports... plus approximately zero (I counted, twice) TB3 peripherals that you can actually purchase. USB-C is a bit further ahead (apart from the Dells and the Gigabyte , but not much. Even Microsoft haven't gone USB-C on their new Surface Book. A few motherboards (mostly the higher end gaming versions for some reason) have a solitary USB-C.
Knowing Apple, they won't jump to TB3 until they can replace
at least both TB2 ports with combo TB3/USB-C and completely drop USB A (at least from their laptops so they can move to a tapered case design). At the moment, that would mean that any external displays would need USB-C to DisplayPort/HDMI/whatever adapters and any Thunderbolt 1 or 2 devices you owned would need Unicorn's horn to Mermaid's hair adapters (i.e. all I can find via Google is the statement from Intel that Thunderbolt 3 to Thunderbolt 1/2
will be available).
So, basically, if you
want to get into USB-C/Thunderbolt 3, I'd give it a year anyway...
At the moment thunderbolt 3/USB C are only any good if you are planning on running a second 5K screen or external dGPU, otherwise they'll make no difference to you whatsoever.
...and there's no actual products available now that do that anyway. The one 5k display that
is currently available from Dell uses dual DisplayPort connections and that ought to run on the iMac 5k.
Thunderbolt 3 will be Display port 1.3 compatable and will mean you can drive a 5K screen through one cable
Actually, its really confusing:
DisplayPort-over-USB-C supports DisplayPort 1.3 (which can do 5k over a single 4-lane connection), whereas
Thunderbolt 3 only supports DisplayPort 1.2 (but can carry two lots of DP1.2 data over one thunderbolt cable). Both DP-over-USB-C and Thunderbolt "Legacy" mode work by physically sending DP signals over some or all of the wires in the USB-C/Thunderbolt 2 connector (that's what happens when you plug a non-TB display into an existing TB port), whereas Thunderbolt can also encode DP signals into a Thunderbolt stream, and have them extracted by a TB controller chip in the display (that's how Thunderbolt displays work). Now, since TB3 is going to incorporate USB-C, DisplayPort-over-USB-C will presumably replace Thunderbolt "legacy" mode - except if its being driven by the Intel TB controller chip then it won't presumably, support DP1.3 that way. However, to pull its 2xDP1.2-over-1-TB3-cable trick, it will have to use 'DP-over-Thunderbolt' mode, which means that the display will have to be a Thunderbolt display.
So, will future 4k/5k displays with USB-C inputs be compatible with TB3 ports?
This sounds like a mess to me.