Will Allies be a thing? Well, Gideon’s token definitely helps that cause. But it being an Ally is just gravy if that actually becomes a Constructed-playable archetype. The fact he can immediately protect himself, then become a creature, then potentially pump out one or more emblems in a game makes him easily Standard playable. The original Gideon Jura from Rise of the Eldrazi was great, but this is probably the best Gideon yet.
One thing to point out is that he doesn’t interact too well with Kytheon, Hero of Akros’ flip-side, Gideon, Battle-Forged. You can’t have two Gideons on the board at the same time. It’s not impossible to see these two played together in the same deck, but timing will be very important on when to play them. This Gideon is so potentially splash-able, though, that he shouldn’t be pigeonholed the way that Kytheon probably will be - white weenie or white/X aggro decks.
Obviously, the hype train is going nuts about this guy, which will drive up his price a ton. He’s definitely going to see Standard play, but I see him being on a similar power level to Sorin, Lord of Innistrad rather than being like an Elspeth, Sun’s Champion level of dominance in the format. That’s good but not format-defining. There are so many high-toughness creatures in the format that it’s hard to know how often Gideon will actually be bashing in, but as a 5/5, he trades with Siege Rhino and Tasigur without actually trading - as he’s indestructible. Definitely a lot of potential with this Gideon, but beware the hype driving his initial price through the roof.