It's also worth noting that Henderson is 30 next year and Wijnaldum 29, so regardless of how Klopp adjusts things (either this season or next), it's natural to assume that Keita and AoC could be their successors given that they're only 24 and 26. Fabinho has also just turned 26 last week, so we potentially have a midfield that could all reach their peak together which would be a key factor.
If form and fitness go well then I think over the next 12-18 months we'll see a gradual move from a mostly Henderson/Gini combination to Keita/AoC, which coincidentally would be happening when David Silva will be leaving, De Bruyne will be almost 30, Mahrez 30, Gundogan 31, and Fernandinho 36. Whilst we can’t put too much emphasis on what City do (and they can still spend big, of course), it does put us in a healthy position where a lot of key players are either approaching (or at) their peak at the same time between 2020 and 2022 (Alisson, Trent, Virgil, Robertson, Gomez, Fabinho, Keita, AoC, Mane, Firmino, Origi and Salah). And not forgetting James Milner of course...
By contrast, City will be increasingly looking to the likes of Sterling, B Silva, Rodri, and Sane/Jesus for inspiration and leadership, all of whom are still hugely reliant on David Silva (captain), Fernandinho (vice-captain), De Bruyne (third captain), and of course Aguero (who is 32 next year) to dictate and often win the key games. Of course, having lots of players (including the entire midfield) reaching their peak together is a double-edged sword and we'll have to properly succession-plan and reduce the risk of the kind of collapse we've seen at other clubs after a peak, but I'm sure we'll plan for that.
I think therefore a midfield of Fabinho, Keita and AoC may well be Klopp's ideal medium-long term vision, but the latter two aren't quite ready yet in terms of fitness or form (or game time together) to make the risk worthwhile - especially considering what we've achieved with a Fabinho/Wijnaldum/Henderson combination.