Ability to add conditions (basic markup) in email templates to display different content based on different scenarios. For example, display coupon code if the user's abandoned cart is greater than $100; or if the user has a specific product SKU in their cart then display a free shipping message, etc.

Track how many phone calls come from cart abandonment (or other retargeting) emails. For example, we would include a section on the dashboard that showed the number of calls received per month along with the number of assisted sales (users who called and then ended up making a purchase).

When a customer moves the mouse off the page to trigger an Exit Popup, the client should be able to specify a zone where on the page it moved off of. Top right, left, middle, etc.

Create a new checkout form analytics report that shows each field as a step in the checkout process and where users are most likely to abandon.

Forward messages from customers responding to an SMS campaign to an email address or phone number with the response and contact information.

Add text version of emails (text/plain) in order to help with deliverability.

Whenever a product is out of stock, having an email form field in place of the "add to cart" button that customers can enter their email address in to receive emails when the product is back in stock. There are other apps that do this, obviously, but I personally love cartstack with all of my heart, so I would prefer if they did it. I think one of cartstack's greatest strengths is the reporting dashboard, and I love having all of the analytics in one spot.

Gamification and Spin Wheel pop ups for discount codes are way more effective than traditional "enter email for code" pop-ups. Optimonk is a good example. https://www.optimonk.com/ Could be exit pop or timed to show every visitor, etc.

A real-time feed showing the number of customers (and any identifying information) currently on the site, specifically in the check-out flow.

Include a link with email templates that has a "view web version" on it