Has the battle against HTML emails been lost?
Most newsletters I subscribe to still use multipart, thankfully. If I'm not mistaken, Campaign Monitor and Mailchimp require you to have a plain text version for your campaigns.
Me, I still yearn for the happy days when I could use Mutt and just occasionally spawn a browser if I had to. Apple Mail, which I now use, is appalling, and the only alternatives seem to be either worse, weird, or only work with Gmail.