1. No worse a user experience in any browser;
2. A much better user experience in Chrome;
3. A much better developer experience;
4. A much better server-side platform than V8.
If we get all that, standards or not, I will be jumping for joy. If Dart is that good, it will become standard, either de jure or de facto as alternatives fall by the wayside.Of the four, #1 (a good enough Dart->JS) seems problematic. #2 may be bad for other browser vendors, but if it's good for users and programmers, why should I care? I see no virtue in a lowest common denominator. #3 and #4 are hardly objectionable. Only those who like them need bother.
I don't know how likely this win-win-win-win is, but here's why I'm indulging in the hope. These guys have been gods of fast dynamic VMs since Strongtalk. If Dart is their chance to build what they always wanted, but this time with 20 years of experience to draw on and the institutional support of a Google behind them... well, we have the chance of something insanely great. Greatness sets its own standard.
Comparisons to VBScript and Flash only kick in if what they come out with is lacklustre.