I've seen Messi drop deep enough to create a 5-man midfield of sorts in some matches and also him being the furthest forward player on the pitch using his presence to let the likes of Iniesta and Fabregas do their thing. Correct me if I'm wrong but hasn't Iniesta surpassed the stat
p) of highest assists by him in a season? If not, then he must be very close and there's still a long way to go for the season to end. So, my point is that if anything, Tito is trying to introduce as much variation as possible to the team with Messis' role ( adding different 'key' off-the-ball movements to his game ) and the manner in which the team uses the ball being a couple of examples and if that's what you're saying then I agree with you.
I think Tito experiments with him due to having one eye on the future. Messi won't be able to run as much as he has now in, say, 5 years' time, thus it's easier use his other attributes to the teams advantage like playing more deep or taking over the enganche role Iniesta and Fabregas hold. We were entertaining an idea with a friend of mine of Messi taking over Iniesta's spot just for experiment a few times and see how he does there. It would probably be like having Iniesta on steroids haha.
What comes to Iniesta's assists, I think he's on par with his personal record from last season. He will definitely add plenty more to that tally if he'll remain healthy until the very last game (hardly has, though, but there's hope).
Back to Messi's role, I would for some reason like our midfield and forward line looking like either this:
Busquets
Xavi - Messi
Alexis - Villa - Tello
or this:
Busquets
Messi - Iniesta
Pedro - Villa - Tello
In the first example given, Messi would play in a traditional enganche role with having the freedom to roam when needed, while feeding our forward three constantly with passes and creating goal-scoring opportunities (having a go at it as well, if he's in the right position).
In the second example, he be more of a deep-lying playmaker and perform the Xavi role. Despite of being a bit of a tunnel-visioned player, he still can work on that aspect of the game with the amount of time he has and I believe he could execute this role quite well if given the chance.
But this is just a thought discussed.