A lineup like that (which I do agree with) is not possible because of Valverde and of course because of @BBZ.
Coutinho clearly and definitely was bought as an Iniesta replacement, not as a potential winger. He is not a winger and will never be a good one. Barca doesn't even need an actual, true winger on the left, because Alba does that simplistic traditional role well and he is at least much faster than Countinho is.
And you are right, he needs to play behind Messi, Suarez and Dembele.
But Valverde thinks otherwise, possibly because of his defending potentials, which comes first when the mediocre coach tries to be a tactician. He might be a sort of tactician, but a bad one of that.
So poor Coutinho looks to be fed up, dissatisfied, without any confidence, and has no clue what to play and how to do that, because his actual advantages were not really welcomed and he simply seems to be lost.
People may cry out here saying he MUST show his better part, but I think they don't realize that he is struggling because of the system.
Let's just play a simple thought-experiment:
IF the team plays a spectacular ATTACKING type of game, who are the midfielders?
At present there is Rakitic, who is the only one (besides Vidal) who has "some" attacking veins, but the other two, neither Bouskuets nor Arthur are the ATTACKING type.
Iniesta WAS an attacking minded midfielder and he is the one missed in the middle at present, because the other two are not typical attacking midfielders.
But Valverde prefers the ones running more and defending more, so in this moment we have the MOST defend-oriented midfield of Barca for many years!
That's why IF Coutinho could play in midfield, that would be the only solution for him, as well as for the team... If not, he has to go, because in this "pseudo-system" he has no other place...
It's all about Valverde's system, because he is not the man who "easily" gives up his preferred lineup, that probably he considers to be a kind of vision, but actually he simply depends and wins due to the individual talents in the team.
He has no vision whatsoever. Not even a bad one...
If he was with another team, Valverde would DEFINITELY play a more defense oriented system. That's what he likes and seems to be comfortable with.
He made a GREAT sacrifice this year, when the 4-4-2 that he prefers turned again to a 4-3-3 and probably it just happened because of the pressure from the elderly Barca supporters and making room for Dembele, so the spectators did NOT want to see a defending Barca, after being a spectacularly attacking team for decades.
That much Valverde sacrificed from his mediocre mind, but I guess he still didn't realize that without an Iniesta supplement, a creative, extremely skilled attacking midfielder, this team will be a rather style-less formation, still being able to keep the ball, have good possession statistics, but there needs to be SOMEONE in the midfield who is capable and talented enough to feed the 3 forwards, well, at least we play with 3 forwards by now...