I think it's more complicated than what you guys are suggesting here. Atleast from the few times we played it last year (w/o Bruno, VdB and even Pogba) this is how it went. Breaking it down by phase of play:
--------------- GK -----------------
-- FB -- CB -- CB -- FB -----
------------ DM -------------------
------- CM -- CM ---------------
-------------- AM ------------------
-- ST ---------------------- ST ---
While defending
When we played it last year (against Spurs and City), Rashford, Martial stayed wide but high up without helping in defence. The midfield would shift around based on which side the ball is (you still have two banks of four). Lethal on the counter attack, but has defensive issues.
Some other times, the AM stayed up as basically a false #9 and the strikers (Rashford, Martial) dropped back to cover the flanks. So it's effectively a 4-3-3 with the attacking mid staying up front. In practice, the player staying up changed between Mata / Martial, and the other one covered our RW. It wasn't very pretty, ended up being very defensive.
Defense --> Attack Transition
It was pretty great for counter attacks as mentioned above when both Rashford and Martial stayed up w/o helping the defense. But in general we're pretty good at counter attacks and this will only work if too many players are committed forwards by the opposing team, so not really an option against most of the PL. Maybe if we're a goal up and we want to pack the midfield but still be dangerous on the counter.
While attacking
It will be slightly different than our regular 4-2-3-1 but not by very much I think. Imagine Mata plays instead of James / Greenwood and drifts in to the midfield (in our regular 4-2-3-1) and the end result is almost the same. Extremely narrow, two banks of four can easily constrict the space. Rashford will drift to the left naturally in both formations and Martial will be central. Maybe Rashford's starting position will be more central if we play the diamond.
Fullbacks will be key and ours are not great in attack.