This is a theory I rambled about a lot in one of my 30 Days posts: that Shen Wei and Ye Zun were at least partially aware, though probably only on-and-off with perhaps decades in-between, throughout that time; which would explain both Ye Zun's over-the-top craziness and hatred and Shen Wei's "I've searched for you for 10 000 years."

My personal headcanon is that Shen Wei awakening, Ye Zun starting to stir up definite trouble and Zhao Yunlan being born were all in reaction to the Hallows becoming active again. (I tend to blame the Hallows for a lot of things, lol) I guess it all hinges on when, exactly, one assumes Shen Wei woke up and came to Haixing. My estimate was at least 25 years before the current time, but it's true that there's no evidence against it being later.

I do remember them saying/implying that Shen Wei went to Haixing to search for the Hallows and act as the Dixing-Haixing liaison with the SID because of the increased Dixingren activity up-top? I also kind of thought he must have spent more time down in Dixing - or at least visited more regularly - before he met Zhao Yunlan again and started hanging around the SID all the time, cos I seem to recall the Regent saying something like, "You're rarely here these days, My Lord." (Though I could be misremembering!)

Your idea about Shen Wei's "search beam" touching young!ZYL and leaving him with that sense of familiarity is a lovely one, and I'd love to see your take on it!