Since that's a specific question you asked, what I would say is that as a standalone mechanic, it sounds like it should be fine at a glance, but taking into consideration Bannerlord's current shielding animations and their limited movement range (thus limited shield coverage), there's a potential problem I can see with this being implemented for high level play, and that is that being able to shoot from a lower height would provide archers with an easier angle to shoot at feet from, especially at closer distances.
I can imagine it being like a reverse problem of archers/xbows/weapon throwers jumping over shield users in warband at close range, and shooting them in the head because shields couldn't be moved high enough to block shots or throws like that. I think this could cause a similar situation, except that instead of it being an unblockable shot from above, it would be an unblockable shot from below.
It's been months since I last played Bannerlord, and I can't remember if you could reach the ground and cover your toes with the smaller shields in the game while crouching, but even if you could, requiring infantry to be constantly crouching down to block foot shots, or especially trying to do so while in the middle of fighting other infantry would probably look and feel just as bad, potentially even worse, than not being able to shoot while being crouched.
Some actual current comp players should chime in on the practicality of something like this in the current state of the game, because things may have changed already since the last time I played, or I may be misremembering how the game worked.
In essence, my position is that being able to shoot from a crouched position would be visually appealing, and would feel intuitive, but given how other aspects of the game are designed (in this case shielding), allowing it could be problematic for gameplay.
I think if shield users were given a higher degree of shield movement range while in a non-crouched position, being able to shoot while crouched would be completely fine, and there would be no good reason for it not to be in the game if Bannerlord already introduced crouching into the game. I do think that not being able to shoot while crouched inevitably leaves a sour taste in every new player's mouth who has tried to do it, as it feels unintuitive and restrictive to be unable to do so. It's definitely a part of a conglomeration of game mechanics that TW (or modders) should look into fixing up all at once so that all the game mechanics can mesh well together.