How stable is 0.2? and where did you get the packs with WEBMs?
As someone else put it, stable enough likely for existing players to play, but likely not the best place for new players to start.
And the answer to the second question is the suggestion that started this conversation chain. Support for most WEBM files has been added, but that does not mean that many, or even any, packs have had them added. And even if they have, there is currently nothing being done by pack makers to let people know that they have been added to a specific pack.
Personally I have not used any yet, and am not likely to do so in the near future, mostly because I have issues with very limited space on my Mega, and I need to avoid the large increase in space used that adding in WEBM would require.