Venice has this going for it:
Venice as a city-state is gone
European civilization is confirmed
Exact match of a small part of Venice's flag (on wiki; but Fireaxis has shown to be somewhat lazy) matches new civilization's colors.
The capital in the image is extremely cultured and Venice would, without a doubt in my mind, get a capital UA bonus. The bonus would most likely be culture-related (it was a city-state)
One of the few remaining European civs that is alphabetically between Portugal and Zulu.
The only remaining European civ that has connection to culture and international trade which are big parts of the expansion. Visigoths and Vandals both have nothing to add to BNW and are not known to be fan favorites like the Zulu.
This is my problem with the theories summed up in one nutshell.
1) We do not know Venice is gone. What we have is solid evidence that another CS has it's color scheme which probably means its gone. This is actually the most solid evidence given that it means something has happened to Venice and on the occasions in the past this has happened it's indicated replacement.
2) The colors are not an exact match - they are extremely close but not exact. The flag spoken about is anything but the most commonly represented Venitian flag. Whilst I agree with Menzies analysis and hypothesis here the evidence is purely circumstantial.
3) Whilst it's possible Venice has culture bonuses this is pure speculation.
4) Venice fits the assumption that the two remaining civs are between Por and Zul - we assume the achievement list is alphabetical. Again it's the most likely scenario but not a known fact.
5) We were already told Portugal was the Euro trade civ. Venice has little to do with Ideology and that is being added as well. Italian areas definitely fit as culturally strong states but as we know any civ can appear as a Tall civ on a minimap if thats the way the game played out.
I think Venice is in and I think the evidence you present is probably right but when people throw in words like "exact" and "we know" based on assumptions and theories then we open ourselves up to terrible errors in judgement.
What we have is a very strong hypothesis based on some good analysis from people like Menzies but what we dont have is any solid factual evidence.
I think 90% is the right number for Venice on a huge weight of circumstantial evidence but to rule out all other possibilities on what we have is a mistake. If we had even one solid fact to base our speculation on I'd call it a lock.
No other possibility like Visigoths, Vandals, Tatars, Ukraine or any other choice has anything more than a speculative case so I think the "field" of all other choices is 10%.
I think 90% on a lot of purely circumstantial evidence and some sound theories is a fair estimate.
I fully expect Venice to be in I just have an issue with people making assumptions and calling them facts.