It's not going to be supported by anybody except Chrome, so whatever app you build, is going to cut 3/4ths of the market (plus all the Chrome Browser users that don't download Chrome apps). Most likely Google will keep it around for a while longer since it underpins not only Chrome Browser, but also Chrome OS.

You're essentially in the ActiveX / Java Web Start worlds. It's fine if it suits your needs but it's not the web.