@scoutSF
I concur with your observations re body text and attachments now remaining visible when offline (or in Airplane mode), but losing access to linked or embedded content. Previous "working" versions of the iOS email client did retreive and locally store the entire email content - with images, links and attachments - thus allowing full access to downloaded content when travelling or when network connectivity isn't available (such travelling by air - hence "airplane mode" where all network connectivity Is disabled).
This issue applies equally to both POP and IMAP; this is a problem with local message storage and display - unrelated to network transport or email protocol use.
if loss of embedded content is a new feature, then this is a feature not shared with the majority of email client software. If it's an intentional space-saving routine, then it should be made configurable. In general, only the very smallest iThings suffer from issues with restricted memory.
Since upgrading and extensively testing email in iOS 9.2, I note that some email that fails to display when offline is often visible for the briefest instant - a mere "flash". This leads me to conclude that email content is actually saved in its entirety - but due to revised behaviour (or simply a bug) where embedded content is demonstrably reloaded upon every access; if an active network connection is not available, the embedded content is simply not displayed.
Similarly, this new "fixed" version has new behaviour... whereby the last viewed message is replaced with a " no message selected" banner when waking from a locked or "off" state.
IN conclusion email in iOS 9.2 is less broken than it was in iOS 9 and 9.1 - but it's far from fully fixed.
AS an aside the double capitalisation issue appeared in an 8.x update - but was fixed. It has now returned In all versions of 9.x.