I saw a few of these types of clinics online when I was desperately researching for an alternative to Walgreens which was booked up. We drove by one near Celebration but it looked so sketchy and $$$ - or maybe that's how it looked to us as Canadians (or me as an Albertan so as not to alienate anyone) when we usually enjoy such good, prompt and public urgent care.
I wish Disney would get on board (knowing full well they won't and that it might be due to legalities or liabilities) and find a way to offer this service a la Beeper MD to their guests. What a relief that would be if it was just a part of the (temporary!) trip experience - the day before, you look at your checkout time, your Magical Express times and go get a swab and get one more Dole whip in before you have to leave!