Actually, after I posted this, I found this topic from 2020 and got a sense of your position for such a feature.
In case you are open to discuss the usefulness (or lack of) of this feature, I would categorize tracking pixel the same as “read receipts” we have in WApp, Telegram, or even Signal. Not in the same category as tracking that FB or Google do for marketing and targeted ads. We are already talking with a customer via Zammad. Knowing whether they read the email or not is an additional insight. Not that different from Clearbit integration that Zammad offers.
I would be glad to discuss the possibility of adding this feature (we can add it too), if you are open to it.
Thanks for your time.