That feature was suggested in the past, but many people argued that it will add an extra confusion.
I would suggest using different accounts on your Windows/MacOS. That will serve you better.
Thanks for your suggestion anyway.

It would be great to have several ebay users in a drop down list in the log in field. So when you log in you check yours and thats it. I say this because in my family everyone uses myibay and each time i want to log in i must write mi username and password. thank you