Well joke aside i think he will play big role in defeating Yhwach .
Only way to defeat Yhwach is to blind him maybe Aizen will do that right now . There is no one who can defeat Yhwach with his Overpowered eyes !
Yhwach is simply too strong right now, dat yhwach, but fanboyness aside, I think the best chance at defeating yhwach is too get a soul king related power-up, as seen only the soul king can obstruct yhwach's precog, so maybe ichigo will be gifted with that, Aizen will most likely be taking on jewgram as we still haven't seen the furthest extent of his abilities, Aizen and shunsui vs jewgram would be pretty amazing, heck Aizen alone vs Jewgram is satisfying.
Also has anyone noticed how like the soul king has a right hand, Yhwach has a "right hand" namely jewgram or the other Quincy gifted with "A" (I refuse to utter his name), it's funny how similar but yet how different the soul king and Yhwach are.