Karen, I don't see any reason why Marketo should not support Google 'Quick Actions'. However, currently Gmail has quick actions for activities like RSVP to a meeting, View Video, open any document in Google Docs folders.
Quick Action in Gmail will certainly reduce the open rate slightly as well. I suggest you add your CTA right next to your email subject line. I suggest trying A/B testing for your email campaigns and see what woarks out best for you.
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