Just realized something...

[Avery Namikaze]

Hagoromo purposely put the markings on their dominant hands and they obviously can transmit some form of power through them. I think this was purposely done to enhance their Rasengan/Chidori as they'll be able to infuse them with the energy, what do you guys think?

Edit: Also just came to me! If the energies they control are Yin/Yang it might create the Omyoudon when they combine attacks, just another possibility.

 

[Made in Heaven]

Seems like it. Kishi's gonna have the finale be just that

 

[Grammar Nazi]

We have already seen the infusing of those 2 techniques and also FRS and Amaterasu.

But you could be right and they might very well be symbolic.

 

[senjuBankai]

so their new power is again rasengan and chidori.??

WTF.!!.

 

[Avery Namikaze]

so their new power is again rasengan and chidori.??

WTF.!!.

Well I don't know, I'm not Kishi. This is just a guess

 

[kyuuubi]

They could have this powerup...

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@underlined it also explains how naruto can give life to gai.
@box could be sasuke's next powerup.