One cometh, one goeth away.
Correction: they do offer dry-cleaning services.
503A is now occupied by R & G Quality Alterations and Tailoring and is now up and running with some signage and a phone number: 617-764-0420.
503B, on the other hand, is now vacant and looks like a decent size space if anyone is looking to open something.
Still no word on the other new openings (517 and 499 Medford) and little to no action seen at their space. If you know anything, feel free to comment below.