Better editing tool and customization of email templates
The option for editing or customizing email templates today is not very good. The problem is that you either have to use the default template 100%, or you have to create the template from scratch in HTML/CSS. There is no middle ground if you just want to make small changes to the text in MEWS' default templates.
If you choose to build the email templates from scratch, you end up with a lot of HTML and CSS from MEWS that you can't avoid. For example, the logo appears at the top of the email along with some text at the bottom, and when you look at the code, there is quite a bit of other HTML and CSS that conflicts with what you insert yourself. The CSS for buttons that you add, for instance, is not the same as the one used in MEWS' default template. For example, the {ManageReservation} button looks fine in Outlook 2016 in the default template – but if you use the button in a customized template, the button appears incorrectly in Outlook 2016.
If MEWS could integrate better editing with, for instance, drag-and-drop elements (like beefree.io), it would be much better. Alternatively, they could try to address some of the other issues mentioned above.