Definitely email clients need to evolve. It's ridiculous that I still have to build email newsletters with table designs because CSS is not well supported. And in this field GMail is actually terrible, not even supporting well the background attributes... sigh.
I don't know if this means it's time for more competing space in offline mailclients because we're seeing a shift to the in-browser emailclients.
Accompanied with that shift moving to HTML5 & CSS3 compliant browsers is priority #1, as always.