Are you really trying to backdoor Venice right now
Eh, it's my idea so allow me to defend it a bit. I don't care about Venice more than the other Italian cities, but I do think that it was the first northern Italian city to rise from the post-Barbarian invasion mess and become a notable power in its own right, thanks in large part to trade with Byzantium, and possibly helping jumpstart the other cities in turn. The current setup, in which northern Italy is either a bunch of independent cities, or controlled by foreign powers, until the Lombard League, is... it's okay, I guess, but it's skipping over a lot of interesting history, it makes it too easy for France/the HRE to control the area (which was the concern I was specifically addressing here), and also the Lombard League doesn't feel like such a pivotal event in real history.
But, and I insist on this point, this change would only work if we came up with a mechanic that forces or greatly encourages capital changes. Nobody here wants Venice to be the capital of the Italian civilization for the entire game. If Italy had a "Power of City-States" UP that gave it a free capital change every 5 techs or something (I'm spitballing here), or some other mechanic, then that would lead to a more interesting Italian gameplay experience IMO, since we'd see Milan, Florence, Venice, Rome etc. all serve as capitals at various points.
Also, an earlier spawn with a single city, no flips, and only a small initial army, would make the early Italian game more fun and challenging: you're just a small city-state, by default weaker than the other European powers, and you need to acquire other mainland cities (or Venice's maritime empire if going that route) through significant effort and strategy.
I wouldn't create a Venice-themed UHV, either. I don't want the civ to focus more on Venice, especially from the Renaissance onwards. It just so happens that Venice is where post-Roman Italy first started to grow powerful and rich.
Like Dracosolon, I don't really expect this to happen, but I think there's a lot of potential in the idea. As a bonus, it would make people stop asking for Venice all the time!