Welcome to QuickBooks Community, elitefireplace. I recognize the importance of having the ability to confirm that the sent estimate was already viewed by your customer. With this, I'll ensure you can send feedback so your suggestion is forwarded to the Product Development Team. 

For now, we are unable to provide a specific time frame as to when the said option will be available in the future. I suggest going to the Gear icon in QuickBooks Online. From there, you're able to choose Feedback to submit a request about having the option to see if the estimate has been viewed by the customer. Any recommendations are sent to our engineer for consideration in future updates.

Lastly, you may refer to this article to understand the new setup of Estimate and how it works in QBO: Create and send estimates in QuickBooks Online.

I'll be around to help if you have any other questions about this concern or any related matter about the estimate. Just let me know by leaving a comment below. Have a nice day ahead, elitefireplace.