Firstly, I don't think night vision is the biggest concern Jorb/Loftar would be having right now with custom clients, but I'll address flaws I see anyways.
There are difficulties lowering field of vision I'd assume with the current system in a way which custom clients can't combat, but besides that the way you're basing how it's affected by stats is bad, since that really alienates newer players who haven't been able to gain serious FEPs. Why should a fresh noob have to suffer if he starts during the night? You need to think of how this affects all tiers of players, and the way you're suggesting this isn't
sholto10 wrote:but could that be influenced by your day/night beliefs slider?

Well then what would the alternate benefit for day be? And how would this relate to caves at all?