This is more of a fantasy right now IMHO
We don't have the RB or the CM to do this,and considering all names in the market it is very unlikely we will ever have.
And the switching thing will cause even bigger problems,Rakitic switched a lot,but it always ended with less midfield control and a vulnerable right side, a player like Silva will make those problem even way way bigger,because he does add little control and defense to midfield,you are basically adding a weaker defensive RW when Messi switch and at same time leaving the midfield with 1 DM and 1 CM on left side and will leave our RB isolated in defense,In other word we lose midfield and right side once you lose the ball, we will get punished by every half decent team.
And even on the offense it won't work,again you are ignoring the most important factor of them all: Messi himself
I think you need to face a simple ugly truth, Messi gets what he wants not the other way around,Messi wanted to play in middle and get Ibra out of the the way:Ibra moved to the right side,It only took a new coach who was a club legend since Messi was a teenager and a new super star signing striker and a trophy less year and struggle during the early of the season to Messi to buy into being a RW again,less than a year later he moved back centrally,looked good for couple of months until Zidane punished us for it in the Camp Nou, over one year later he is still playing centrally.
4-2-3-1 is far from perfect, I have been always a guy who rooted to 4-3-3 to the extreme but the current situation is basically hiding from reality,I simply can't see Messi moving to RW on permenant basis,it is a thing of the past and the longer we pretend that it could even happen again the more we are shooting ourself in the foot
It can work in some conditions. First conditions would be to get back to pressing after losing the ball. Imo, if you find a way to narrow down the space the opponent has and you press, the defensive issues of the players are not as evident simply because there is density around the ball and the opponent finds it very hard to create a 1 vs 1 situation. This is actually what happened under Guardiola. We defended by pressing, and by position, not by having good defenders on the field.
So, imo we have two options here, going forward, and depending on what we want to do we need to plan ahead and to implement the right tactics. Both these options can lead to great results, but the style of Barca in recent history has been associated with fluid football.
1) It's either we get back to a more fluid system, like in the pictures I posted, in which case everybody will have to do the defensive phase. This is very hard to do atm, I agree, because it takes a lot of team effort to be able to defend in 10 players, and attack in 10 players. In fluid football, attack and defense are not totally separated from each other. In rigid football, they are, in the sense that you would see players (one, two or three depending on the system) doing nothing to help out, because... well... they simply have no role in defense. That means the opponent finds 1 vs 1 situation easier, in which case it comes down to the player's individual defensive quality to stop actions played in their zone.
So you have defending as team (fluid), with roles that change depending on the position of the ball, and defending simply based on tasks and roles associated to each position. In the first case (fluid one), you can use players that are not natural defenders, because the strenght is not in the player, but in the system. In the second case, you need to find players who can simply do the job, as the success or failure of the rigid approach is in the sum of the players' individual qualities and how those qualities match with the tasks associated with the positions they play in.
2) We continue to play conservatively, like 90% of the teams play. In ths situation, it becomes very hard to implement players like Coutinho and Silva, because they need to be better in defense as you say.
So, the 4-2-3-1 is a solution if we are going to play with little movement (that's what I mean by rigid and fluid). It is a solid setup which would probably help us defend better.
But I like fluid football more, and it is a style of play which is gaining popularity right now, and one that suits us very well. And the amount of movement in our positional game has decreased with each season that has passed under Lucho, thus exploiting more and more of our inability to defend in a conservative way.