Before launching the public beta, we had the WooCommerce Checkout Optimization plugin tested with popular WooCommerce themes and plugins and were pretty confident that we’ll be able to achieve what we wanted. But as more and more users started using it in their stores, we started getting a steady stream of compatibility issues ranging from layout glitches to disappearing elements.
Most of the issues would be because of the theme and some because of other plugins. As we kept fixing issues that we could, it was getting apparent that this is not something we could keep doing with the thousands of plugins and themes that were out there.
In hindsight, the template route was not the best decision. We knew we had to recode the whole thing from scratch without the sort of dependencies we had baked in with building the plugin alongside the default WooCommerce checkout.
To read about my thought process regarding another major decision with giving control of enabling and disabling the optimizations to the user, read the Too many options, too many decisions post.