I'm on the side that takes the wording of the achievement as near-certain confirmation that Italy is in. Now, I've been vocal about my support of Italy being in, but I'm saying that if the wording had gone the other way (i.e. the achievement had been worded without the SfA qualifier, as with Belgium) I'd be sure that it wasn't in. This sort of leaking is not at the discretion of a state-department clearance - it's meant to get us into a tizzy and talking about the game more excitedly*, and so that's where I am with this.
I would love to see an Italian civ since it would be hilarious what kind of BS Unique Ability it has to occupy itself during the Ancient/Classical eras where it pretends to not be the center of the Roman Empire. This is because presumably any Italian Unique Unit or Building would come at the Renaissance at the earliest (to avoid connotations with Rome), so the Unique Ability would have to cover the earlier eras for gameplay purposes - everything about it can't be Renaissance-based. Maybe something Etruscan? Or is that off-limits for "real" Italy too?
Italy would hardly be the only civ to have it's Uniques centered around a single era. Look at Babylon, whose bowmen and walls are both Ancient era, and whose UA, while lasting game-long, is also centered around the ancient era (i.e. getting to Writing early.) The Huns similarly have a fully-ancient focus. Rome is fully classical.
Now, a fully renaissance focus is a little different than an ancient one, to be sure, but such a thing is neither unplayable, untenable, nor an impediment to enjoying them or gaining an advantage with them. It just means playing with that certain aspect in mind. Particularly if Italy has a Great Works focus, as Louis XXIV has suggested and seems likely, then owning the renaissance in order to secure a later culture victory makes a lot of sense.
In another (highly unlikely) UA set up which I've spitballed around here before, imagine if the UA is that Italy alone may have the Piety and Rationalism trees open simultaneously. That would be both accurate to their history and legacy, and encompass both Medieval and Renaissance eras without betraying the civ, while lasting ever after in the game in fruitful ways, and yet even the fact that it takes a while to come up wouldn't hurt it as a UA, because in order to make the most of it one must plan to use it properly in the early stages. Hell, consider the current French UA, which craps out in the Industrial Age. I'm sure there are lots of ways that a civ can fail, but being centered around a single historical era isn't one of them from what we've seen so far.
*(which I'm totally cool with, by the way. Firaxis and 2K and Aspyr don't have to tell us anything, really. If they had just dropped by in July to say that there was a new expansion and come get it, those of us here would have done so. This way, they are able to generate buzz via their fans and also get our feedback, and also hopefully bring in new fans, who can also be part of the conversation and help to come up with more and better ideas, more and better mods, etc. It's a good system and has kept me and a lot of other people consistently excited during the waiting period, so I'm in favor of it.)