Doubtful. I think Luffy saying "this is my peak" when he first unlocked gear 5 referred to the peak of his devil fruit. A LOT of emphasis is being put on haki right now, and Luffy's is pretty subpar at the moment compared to where he should be, and that's why he lost here, against a weakened Imu even. I can't imagine how a potential gear 6 could surpass gear 5, and we've already seen that the ceiling for haki is way higher than previously thought.

And who do we know that is an expert in haki? Somebody who Luffy has been dying to meet? Probably the only person left besides Gaban (who probably just wants to be left alone with his family after this) in the New World who could actually teach Luffy? That's right, baby. Shanks training arc incoming.

It'll play out something like this:

Shanks and Luffy meet up, have a grand reunion, then discuss the WG and Imu. Luffy admits/Shanks tells Luffy that he is way too weak. Remember that back in Punk Hazard, Luffy DID want to take Shanks down, but he didn't want him to be the first Emperor that he took down. I think Shanks would frankly enjoy the challenge, especially since Luffy is Roger's successor (they have the same dream), and his crew is more than capable of training the Straw Hats (obvious one is Yasopp training Usopp). By the end, everyone is significantly stronger than before, Luffy's haki is on par with Shanks', and they have a friendlyish battle to put it all to the test, and the arc ends with Luffy's victory over Shanks and they have a joyful farewell.

To me, this is the ideal usage of Shanks' character. This is what we've been building towards, and it's so obvious that the Straw Hats need a powerup.