(This would be for those of you who edit on laptops w/o a secondary monitor)
I had thought the solution to working with today's wide-gamut displays was to profile the screen (ie SpyderX, Xrite) targeting R709 and then you're done, but apparently this doesn't work at all -- as far as I'm aware, you cannot correctly emulate/clamp to sRGB or 709 via icm files (which reinforces my sense that color management in windows is basically hopeless).
The goal is to correct the mismatch between what Windows/Vegas expect (an sRGB display) and how your wide-gamut monitor displays sRGB colors (wildly over-saturated).
So I've been pondering workarounds.
1) You could get a secondary (broadcast) monitor. Not a solution, if you want the portability of editing on a laptop, but worth mentioning as it is a simple and effective solution to an otherwise intractable set of problems.
2) Create and apply a LUT to Vegas's output fx to convert your preview to sRGB and/or R709 and then trust that your preview is correct.
DisplayCAL should be able to do this, except profiling wide-gamut displays with colorimeters is tricky, and DisplayCAL itself is complicated. This is probably a good solution if you're able to get it work, but there is a non-trivial chance you create a LUT which just shows you another, incorrect, preview -- and you don't really have any way of checking it unless you've got a spectrometer.
3) Just live with it.
Wide-gamut displays on windows are becoming ubiquitous, so if you're delivering to the web, you might reason that your preview actually matches what most of your viewers are going to see. This does seem a little nihilistic, though.
4) Use an sRGB/R709 emulation mode if your laptop/display support it. Dell offers the Premiere Color app, which does this job for its XPS laptops. Unfortunately, DPC breaks and/or is broken depending whenever windows, your video driver, or your intel drivers get updated. No guarantees DPC is accurate even when it is working. And most other makers (as far as I can tell) don't offer true emulation modes.
5) Get a laptop with an sRGB display. This unfortunately probably rules out 4K displays, which is probably a dealbreaker. Even if you're willing to buy another computer *and* go back to HD, you'll probably find non-wide-gamut displays only on cheaper, weaker machines, and screen quality isn't likely to be great.
6) Use Vegas' color tools to correct your preview window to an image which you know is being displayed correctly.
Put an image on the Vegas timeline; open the same image in an app you know is color-managed (ie Photoshop, Firefox, ...). Put both apps side-by-side on your screen, and correct the Vegas preview to match the color-managed preview.
Obviously, there are lots of potential pitfalls here, starting with whether or not your target image is actually being displayed correctly (see: colorimeters and wide-gamut displays). Maybe the safest solution is to just use the Vegas Secondary Color Corrector to turn down the saturation until it matches the sRGB image. On my screen, a desaturation of about .708 seems to match. You could also correct the gamma to match R709's slightly different curve.
Export your corrections as a LUT for future use -- and don't forget to turn this off when you are rendering!
The advantage of using your eyes to desaturate is you are getting a good sRGB emulation, at least in terms of saturation, which is probably the biggest problem (switch the fx on/off to see just how big the difference is--it's huge).
A disadvantage of this method is everything else on your screen -- and your windows desktop -- remain oversaturated, which may pull your eyes in the direction of adding too much saturation to your edits.
7) Wait for Windows to correctly interpret wide-gamut displays. This could be a long wait.
If anyone out there has another workaround for wide-gamut displays, please let me know.