I think the word 'dead' can be confusing, because the hackery meaning differs from the ordinary meaning so much. None of those technologies is 'dead' in the sense of 'defunct.' But 'dead' meaning 'on a road whose only endpoint is obsolescence'—I'm gonna say Silverlight and Flash are dead.
Full Standard implemented by vendors takes exceptional long time. It is very frustrating. Developers have to deal with numerous compatibility issues. So it is too early to say either Silverlight or Flash is dead.
Even if there is a mature JavaScript library and framework that comparable to existing Silverlight and Flash. It still takes long time to change. Companies and developers investing heavily on one technology will not adapt new technology very soon, considering that large base of existing software, human talents relies on that technology.
If you're going to make something as progressive as a web-based DAW, make sure it has a future, even if it's not quite ready for the present.