The only problem with that is that there is a LIMIT (3) on how many times they can be prompted unless they put in the special Covid provisions again. If you want to promote them a 4th time, they are then subject to waivers if they're sent back down. And the Patriots have lost more than a few players to the waiver wire over the years.
This idea that they'll only keep 8 (which has only happened twice since Belichick got here and only because of late injuries) says exactly you has been paying attention over the past 20 year.
Depending on where McGrone is in his rehab, the Pats can put him on the NFI list as soon as he's signed.
I don't think the 53 is going to be as "tight" as you think.
Guys on the outside looking in (IMHO):
JJ Taylor, Dan Vitale, Matt LaCosse, Najee Toran, Korey Cunningham, Yodney Cajuste, Isaiah Zuber, Devin Smith, Kristian Wilkerson, Tre Nixon, Bill Murray, Tashon Bower, Carl Davis, Nick Thurman, Akeen Spence, Bentley, Jennings, Hall, Michael Jackson, Dee Virgin, Myles Bryant, Brandon King, Roberto Aguayo, Brandon Bolden, Devin Ross, Marcus Martin, Montravious Adams, Rashod Berry, Brandon Bolden