User blog comment:Kirkburn/Technical Update: April 13, 2015/@comment-452-20150413202500/@comment-126761-20150414133439

The new email system is a significant change from the old one - so it wouldn't be a simple case of porting it over. Every time we work on upgrades, we have to make a choice: what does it make sense to spend time on? Now, I'm not saying that plaintext emails are definitely 'not worth it', but we have to balance the need for improvements versus continuing support for increasingly niche formats - similar to how we cannot support old versions of Chrome. There's a point at which it simply doesn't make sense any more.

Regarding images: we've specifically designed it that clients that block images would see only a minor impact on the email layout.

We'll certainly make sure to discuss this further today.