The Klopp system clearly requires that the two wider midfielders in the midfield three are tireless workhorses. This ultimately allows the front three to play higher up and closer to each other, essentially making it a proper 4-3-3, instead of the 4-1-4-1 you often see out there.
Thiago doesnt really fit the mould. However, if he did come in, you could possibly see Thiago taking the deep central role, and Fabinho moving to the 'carilero' position with Henderson. Then Klopp still has his two midfield workers and the passer from deep. Like this
Thiago
Henderson Fabinho
I'm not sure Fabs further up the pitch works so well.
To be honest I don't fully also get the idea how we have formed the idea the Thiago is a slacker. Klopp managed to fit coutinho in his system...so he will find a way for Thiago more easier than that.