Ah... so the Meng who are having that friction with the Bai and maybe not being so on board with Shenhua's moves are also representative of the Weilu clans who Ling Qi is specifically here to provide a bridge for... and lo and behold, she's serving in that purpose here. Lady Meng, then, takes that opportunity to (hopefully) introduce another Weilu-aligned young man to the inner circle (and possibly tries to dangle him as husbando-bait for Ling Qi, as a fallback plan). I think the husbando aspect is less a part of why he was picked, though. He'd have been picked to be at about the right age and cultivation (thus fitting in with them socially while also showing at least comparable levels of potential) and after that being particularly useful in the current mission (from having quite a lot of lore pertinent to the coming mission specifically) while also filling a role (general sage and informational support) that CRX does not currently have filled in her inner circle.
I suspect, then, that Xia Lin is similar, in some ways. She's noted as being the first Xia to meet the General's exacting standards as well as being the best of the General's soldiers in CRX's generation. I'm not sure that the General is trying to weave her into CRX's inner circle directly, or at least not soon, but the combination suggests that there's a good chance that she'll eventually wind up at the head of the White Plumes (or whatever it turns into) and the General is trying to set her up for that by putting her in a position where she can build rapport with CRX and her current group. It's also entirely possible that Xia Lin is someone that Shenhua might select as one of her forced picks, should our little protagonist set fail in the missions she has assigned them, and I suspect that the General is setting her up for that as well - in both trying to improve rapport and in seeing how much rapport is there to improve. Unclear how many of the strings on this one Shenhua is holding directly.
I will note... if CRX does wind up pulling Meng Dan into her inner circle, and Shenhua isn't given any excuse to meddle with its members, our group is going to be really quite politically unbalanced. We'll have two uplifted commoners, one of whom is moderately aligned with the Weilu, one Weilu lord, and Bai Meizhen. The Bao have their potential in, at least for the moment (one suitor openly, one less so) but the more imperial-aligned clans are going to start noticing that their "voice to the heir" slot is filled with a whole lot of basically nothing (other than what they can pull through Gan Guangli... and in many ways it seems like he's more interested in the lower-tier types... especially if he does manage to successfully woo Best Fox.) At that point, we're absolutely going to be seeing those clans trying to inject their own influence.