Looking at Henderson's decent assist stats this season, and generally how he plays, it's worth considering his position.
In a classic 4-2-3-1 model, would it not be wise to move him from the '2' into the '3'. Could he not play a Dirk Kuyt role, except with more movement, pace and assists? That leaves Milner to occupy a more reserved, controlling role in the centre alongside a DM in the '2'.
In our standard 4-3-3, I suppose Milner and Hendo could sit alongside each other in front of a DM, but it means pushing Coutinho into a wide forward role, which isn't ideal.
On paper, it's a wide forward role, but we've seen in his first season it doesn't work out that way on the pitch; same when at time Suarez was starting on the left / right on paper - essentially, Coutinho plays as an inside left who drifts in often and pulls out wide at times, while Sterling / Ibe provides width on the other flank. Defensively, he helps out on the wide side again. I suppose Moreno (or whoever is at LB) ends up motoring up to help provide outside support for Coutinho. What this gives us is solidity in the middle with a DM (say Lucas, or when Can has improved enough defensively) sitting behind Henderson - Milner, both of whom are able to win and retain the ball, still create chances (not as sexy as Coutinho of course), while still having the workrate as well as physical presence. It isn't a sexy-looking midfield trio, but I like the solidity and balance of it.