Sorry, but I really doubt it has to do with lag. As others have mentioned, it's just a number. There is no possible way a static number in memory could affect lag. What causes lag is when information is sent to and from the server, and in regards to loot, I would speculate only occurs when someone collects a piece of loot or requests to see how much loot they have through showloot. These actions' performances are not dependent on the amount of loot an individual has.

I'm fairly certain the loot limitation was put in place to force players to sell their loot. Dusty said he's trying to gauge how this change will affect the economy and whether or not he needs to make further tweaks. I assume it would be pretty difficult to determine the effect this change has if people refuse to sell their loot and just hoard it all instead.