I would like to propose these 2 features:
SendFox (Email Service Provider) and Brizy (Page Builder) Full integration.
They both provide API access, senfox works with notes instead of custom fields, but it should work neverthless for dynamic content based on the info stored in sendfox database.
A lot of people is moving from AC to Sendfox due to costs mainly and because they are running a LTD.
Please try to make this happen.