Treaty of Venice

Am I right in thinking that the Treaty of Venice, which limited the power of magic items sold to mundane people, has been left behind in this edition, and replaced with the bit about 1 magic item per year, more if you are in Rome?

I don't think so. The treaty of Venice only applied to the Roman Tribunal if I recall correctly, and there has been no need to revise or leave it behind as of yet. I do think that the ruling we have in 5th edition was based on the treaty of Venice. In fact, you could play it where the Teaty of Venice came first, and the newer rule was made at Grand Tribunal at a later date. Or maybe there is a conflict in rulings, most tribunals do it one way, Rome does it a different way. That could lead to some interesting stories of conflicting cultures and goals.

Page 16 of the core book speaks to this issue a bit.