I think today we *require* complex timbres... we won't be satisfied without them... we have to push the audio envelope.
Instruments always follow the technology of it's culture. Look at Aboriginies, low tech = click-sticks and hollowed logs. Today we, at last as artists, will push the bits of computers to their max for new sounds to inspire us.
Now, these sounds may or may not make it into the commercial mainstream. That too depends on the culture and the song the sounds are contained in. I think most pop music now does a wide job of using complex sounds as backing instruments & beats. Bitney Spears and Outkast have someone cooking up funky tones for their songs.
As I mentioned above, I tihnk the most complex timbres will find their place in commercials as there's only a little time window to find the hook for the viewer. Today's youth market needs an full-on emotional sound experience with their product, not just a signature "company sound logo".
As far as the future of EM... it's gonna look like the last 20 years... there will be a few great artists who create fascinating stoires with these new tones and then there will be dj's who mix them, there will be big-time producers who use the style of the time to sell the latest teen-pop drival and there wil be kids looking to hijack technology in their quest os sonic rebellion.