You could try putting a suggestion here: [email protected]
or
if you are a Pro-user try here and raise a ticket:
https://www.emclient.com/support
Personally, I suspect there isn’t a great demand for this feature but worth asking I guess.
At least you should get an answer one way or another and decide whether to revert to Thunderbird. Having used eM Client after using TB for years I’d never go back. In my opinion this product is much better and cleaner.