@twisted1919 Following features may you consider in future release.
1- Drag and Drop Builder, it should be core part not as any external extension.
2- Global or Single List Segmentation based on activity i.e. Who open email or clicked a particular campaign or link.
3- Customer message replace with email alert i.e. To send email right from dashboard to customer just like any simple CRM.
4- In Monetization - Each plan may have unique link to place order independently rather than any default sign up plan.
5- In Monetization - Another sub menu Invoices can be created for easy invoice tracking, reminder and management.
6- Geo location statistics can be enhanced.
Also in world of email marketing List cleaning service is also very popular if you can develop an app like Mailwizz it will be very useful and popular similarly SMTP gateway can also be developed as many business now prefer to offer SMTP service as well an SMTP gateway can be a dashboard where SMTP user can see statistics of mail relay, bounce and other useful statistics.
Thanks for your attention.