Not a big deal
Considering the problem is not that it is a vendor-prefix but that it is a vendor-prefix from another vendor (out of the control of the MS team that builds the IE engine) this can be easily solved. The IE team can just use the exact same implementation as the Webkit team but call it -MS-text-size-adjust.
In the linked blog post...
They said they'd already done that.
MS get it wrong when trying to be nice.
Well who would want to be dependent on third party proprietary extensions like Flash? What? oops I mean webkit.
MS: throw in the towel...
Alternatively, MS could just do what it should've done years ago and dump its trident rendering engine (which is behind the IE6-9 and, I assume, this Win mob IE) altogether and adopt a real, standards compliant (and then some) rendering engine built by the open source community like Webkit or Gecko. Doing so would immediately remove their massive functionality and web standards compliance deficit, and give them a chance of having a credible browser, which would be a big win for all involved.
It would even be a big win for Microsoft, seeing as they wouldn't have to keep burning cash to keep building the train-wreck that is trident.
Microsoft!.. The code exists. It works. It's free. - Not to mention the massive surge of positive PR you would get for adopting it, and the positive effect it would have on the web as a whole... Why do you resist?
Your all about an "open web" now, right? How about a "little" demonstration of that attitude?!