Whither ECE?

This is a question for those of you out there who still have Exchange Client Extensions.

Aside from budget concerns and legacy support, what blocks you from re-implementing your extension as an Outlook Add-In? Specifically, I'm looking for events and capabilites that would have to be added to the Outlook Object Model to allow you to migrate your code.

For example, ECEs have an OnRead event that happens before Outlook reads from a message. This allows the extension to modify the message first. The OOM's Read event happens after Outlook reads from the message, so it's too late. You would need some sort of BeforeRead event to match the ECE.

Can you come up with more? I've got a list I put together here, but I want to see what you folks have actually run up against, so I'm most interested in real world examples drawn from your own code. Thanks!

[Update: 11/21/27]

Welcome viewers from Patrick and Randy's blog! I've seen a few comments that indicate support for legacy clients is a major concern. We definitely understand that and it's on our list. But what we're looking for here is things that you're doing with ECEs right now that you cannot do with Add-Ins. To put it another way - if ECEs suddenly vanished and you had to implement your code in an Add-In, what missing features or capabilities would be showstoppers?