I hope this will lay to rest the myth that it is impossible to buy coffee with bitcoins.

The ideal solution for Starbucks would be some kind of Lightning Network enabled Bitcoin wallet, because that is more suited to quick and inexpensive micro payments.
I hope this is not just another "test run", but a full implementation this time around.

I know KFC and McDonals has also had some trial runs before, but it was more a promotional gimmick than anything else.

, would we see the billions of coffee drinkers all around the globe start using bitcoin? Would they buy bitcoin only to purchase coffee? Would they stop using their credit cards?
No. But if they did then we might see blocks become full and fees become high again hehehe.