When Google disabled this feature in late 2013 for the desktop and early 2014 for mobile clients it was pretty much the last straw for me - their "promise" that they'd figured out spoofing and spam didn't sell me (I was a Google Apps client for my small company). This isn't a rant, but it pushed me toward Office 365, which I'm on now and now why I use Gmail only for junk now. My iOS workaround was to use the paid Mail+ app but that's abandonware in that it still doesn't support secure connections and 2FA properly - my Office 365 and Gmail accounts block/reject the app as not secure.
I haven't found any mobile app that doesn't download images on an email outside of the native Nexus Mail client; Google originally removed the option from the native email client but restored it shortly thereafter, likely due to a lot of griping.
FWIW, I also use a modded Windows Phone, a Lumia 640, modded to run Win 10 Fast Ring builds. The Mail client includes an option to block remote images, and it does work perfectly - except for Gmail accounts, which load remote images whether the option is enabled or disabled. Sorry, I've got nothing more...
