The problem we'll have with a 3 at the back over the long run is our full backs aren't wing backs, to play 3 at the back successfully ideally you want wing backs who run the flanks with great attacking output, you could argue Shaw is just about passable, but Wan-Bissaka is nowhere near being a wing back. The 2 in front of the defence assuming it's Fred and McTominay will have their usual problem of breaking through the lines too, leading to us struggling against the press. This lack of creativity would likely be more noticeable if we try to play the formation in games where we're going to be expected to take the play to the opposition, who won't just leave the huge gaps Tottenham did today (especially for the 2nd and 3rd goal's).
Problem looking at the bigger picture is we simply haven't built a squad with this formation in mind, so it's very clearly off the cuff. We've spent 2 summers chasing a guy we spent £73m on that would have no real role in such a formation, we spent £50m on Wan-Bissaka who isn't a wing back, and to not upgrade the midfield would be criminal if such a formation was the plan.
I don't see any reason why we can't try 4-4-2?
I can't see any combination of a midfield central 2 that would work. To play 4-4-2 this day and age you normally need 2 excellent central midfielders with legs, and/or 1 of the 2 up top has to be basically willing to come into a 3 when defending. I'm not sure our wide players would be suited to being traditional wingers either, they're more wide forwards.
Problem with 442 is the wing positions. They are not very good defensively so it will end up being a 424 or a 415 if you plan on playing Bruno in midfield.
The only practical thing for Ole to do is play a 532. He can rotate Rashford and Greenwood in for Cavani and Ronaldo. Sancho could maybe play the AM position or more likely he could possibly play a wingback role with a Telles against easier opposition. Lingard could come in for Bruno on occasion.
I hope Ole uses this formation until the team get some consistency. He should use the full squad once he gets over this rough patch. He will be sacked at some point but I would like to see him make it to the end of the season.
And what if we never get that consistency. We've gone through many iterations the last few seasons. I remember when we initially struck upon Fred and McTominay and that was meant to be the answer. The problems at the club go far deeper than a formation change, I doubt this formation will change anything on a consistency front.
I'd also argue it's far from being the only practical thing to do with the players at our disposal. How many top managers do you think would come in and also play 5-3-2 with what we have at our disposal? We've never really tried flooding the midfield for example.