I don't think items are actually generated until you trade with an NPC. If you left the game running and came back every hour or two to do a round of merchants, that would eventually cause a problem. Depending on how much crafting is done, it still takes a fair bit of trading, though.
Checking saves for a couple of people who ran into this issue after the limit increase, one was at 575 hours playtime, one at 547 hours and another at 350 (in Luculla Forest, character level 13). That isn't a very big sample size, though, so I don't know what the minimum playtime someone could expect to run into the limit would be, if they did as much crafting and trading as possible.
