Thanks for your comments on the idea. This isn't planned for development in the next quarter. For transparency and clarity, I'm updating this issue to 'Not currently planned' for the time being. We are investing in bolstering our email testing capabilities starting here. If you are willing to jump on a call to talk more about this functionality, and your specific use cases send me a direct message. I would love to chat more.
We will re-evaluate in the future and we will update this idea if anything changes. Please feel free to upvote and continue to leave feedback on this thread.