Why we should care
I'm not suggesting that we can't gain from a digital standard - there's a clear advantage to using a digital connection over an analogue one, I'm just pointing out that single-link DVI (or even dual link) wasn't universally better than the VGA technology available at the time, and that this harmed its market penetration. I'm not against progress, just against the introduction of standards that take backwards steps because the high end of the old standard was considered irrelevant - future-proofing has a way of redefining the "high end". As an example, UDI appears to max out at 36 bits per pixel (although I'm not sure I'm reading an authoritative source); dual-link DVI can handle 48bpp, 8 bits per channel per link. The Canon 1DMk3 has a 14-bit image sensor; if this technology gets into video cameras, UDI requires downsampling where DVI wouldn't.
The DVI digital signal is a direct equivalent of the analogue one (regardless of whether an analogue monitor would cope with the signal, in the case of reduce blanking). This both makes it easy to combine analogue and digital output (the graphics card can throw the same pixel data at a common output component and have the data transmitted in both forms, rather than needing to scan the frame buffer twice) and makes it relatively easy to convert between video connectors. While I'm a fan of the SCSI protocol (and various networking protocols that have proper error correction), even once sufficient bandwidth has been routed to the display (3.2Gbit/s is quite a way under single-link DVI) there's still a need for a frame buffer to reconstruct the image; not a big problem in a monitor (remember to triple-buffer everything) but expensive in a display format adaptor. As I've said of DisplayPort, would it be a nicer spec? Yes, from my point of view. Would it gain us enough to be worth replacing the existing video stream approach? Personally, I doubt it.
It's true that neither UDI nor DisplayPort have any current market penetration; the concern is that, once they do, one of six things happens:
1) The new monitor you want is DisplayPort only, and you have to upgrade your graphics card/the new graphics card you want is DisplayPort only, and you have to upgrade your monitor, otherwise they won't talk to each other.
2) Devices gain yet another port on the back, which adds to the cost and space but essentially gains us nothing.
3) People use an unnecessarily expensive DVI/HDMI/DisplayPort adaptor.
4) The ports are multi-mode, which limits them to single-link support (AFAICT).
5) Graphics cards start being able to run all the standards down a set of pins, and we end up with an octopus dangling off the back of the computer (see some VIVO solutions).
6) Other connectors start to go missing. As someone with lots of CRTs, this lacks appeal.
It does not appear to be the case that DisplayPort gains us anything (except being marginally easier to plug in without seeing the socket, allegedly); in return, it possibly forces an upgrade cycle and definitely causes unnecessary incompatibility and confusion. And this is if all devices talk to each other perfectly (because that worked so well with HDMI and DVI). It seems unlikely that a new connector will make anything cheap, because there'll be years of backwards compatibility requiring *both* connectors.
Other than a few companies, I don't see who DisplayPort helps. Having re-read a presentation on the subject, the bandwidth appears to be slightly greater than HDMI 1.3 single-link, slightly *more* greater than dual-link DVI (assuming dual-link DVI is 330MPix/s, which is not actually a limit but the expected minimum because, for dual-link, one link should be capable of at least 165MPix/s), but substantially less than HDMI 1.3 down a type B connector. It is not, for example, enough to drive a WQUXGA T221 at full refresh on its own (whereas a dual-link + single-link DVI connector *is*), and the "next smallest" common display size (the WQXGA 30" panels and QSXGA medical panels) are well-catered for by existing DVI. Even if increasing bandwidth is not a significant aim for DisplayPort, it seems that a greater step should be taken in this direction.
All this assumes that four DisplayPort lanes are available. Although cables have to support this (kudos for avoiding the "it's a dual-link DVI cable" "so why are there pins missing?" debacle) there's no requirement that devices themselves do. I'll be interested to see how long after devices get the "DisplayPort" tick box it takes for the number of lanes to be labelled, because I bet - just as dual-link DVI took a while to appear - the first batch of products will be castrated to the common range of monitors. One lane can do 1080i; two lanes can do 1080p, and I'll be pleasantly surprised if four lanes are considered necessary just for the happy minority with decent resolution displays; that said, I'm a cynic (can you tell?)
On the plus side, (new) larger monitors are, I believe, obliged to have HDCP support in the US now. I suspect that higher resolution displays will be limited to HDCP over DVI for a while (when nVidia don't break dual-link support), but the HDMI type B connector might turn up eventually, you never know. (For so long as most protected content fits in a single link, if you don't mind your 30" screen running at 1280x800 and you didn't want to view in a window then single link support might not get replaced.)
I can't see how adding another standard to the mess improves matters. If the industry would concentrate on making an existing standard dominant, and maybe improving it in a backwards-compatible way, I'd have more sympathy.
Turns out I had more ranting left in me. :-)