...the idea that they basically swap roles in the time loop, and that Shen Wei is significantly older than Yunlan in current time

I've always thought of it this way, not least because the gulf of difference between YOHE!Shen Wei and our Shen Wei would require, I think, a good amount of time being disillusioned re: the world/people in general and Haixing-Dixing in particular. A few decades of working with the Regent + SID chiefs like Zhao Xinci and trying to make peace with an increasingly-batshit Ye Zun seems like a thing that could achieve that ;D