You're wrong "extend" is when you add features to a standard that are not part of the standard. Since this only compiles to JavaScript and isn't being built into IE, it doesn't qualify. Dart does, though.
Microsoft was so ruthless, and dominating in the 1990's that it will be incredibly difficult to convince any developer that was streamrolled by this company to give them a second chance.
This would still be the "embrase" phase. Extending is when they add a new feature that doesn't exist and isn't supported by the competitors. As soon as you see it compile to a flavor of JavaScript that only IE understands - then will the "extend" phase have begun.
Recently, Microsoft has been pushing Javascript very hard (embrace) and now it looks like they've started the "extend" phase.
Luckily, no one really worries about them being able to pull off the "extinguish" part anymore... they just don't have enough market power these days.
EDIT: Yes, I conceede the fact that TypeScript is OS probably addresses most of these objections.