The end of that Tekken tournament sure was interesting, huh? You've got a lot of questions about the above and here I'll try to make some sense of it all.
Here's what makes sense given known quantities.
Street Fighter X Tekken could be possibly canon to the Tekken series given where things would fit and make sense given the time these events would take place. This is simply because of Street Fighter's ability to see nothing past Alex beating Gill at the end of 3rd Strike and making sure to tell every possible story they can before canon hits the wall that is 2nd Impact.
V has pretty much confirmed 1996 as its date with everything we know now so trying to get that to bend to anything outside of what's already been established is mostly impossible unless you want to retcon everything and nobody cares that much about Street Fighter lore to even dare do so.
For the record given what we know about Tekken is 7 is that it takes place sometime between mid-2016 and sometime in 2017 so again this is why Street Fighter could never crossover canonically into Tekken and deem any canonical crossover feasible timewise without a giant retcon to Street Fighter's events in this universe. Just know that the events of both series could happen as they do and share an universe doing so and work just for the record.
However, Street Fighter X Tekken can be used as a canonical bridge with a small retcon of Street Fighter's already given events in the time when they actually take place. Similar to how KoF's timeline works with anything that predates KoF '94 and how it assimilates everything forward from that point and bends it to its canonical will.
By the by, if they decided to use Street Fighter X Tekken as a canonical bridge is the game's events would take place during Tekken 6 because that's the only logical place it could fit and be a canonical entry given what we know about the story that game provides and it fits perfectly with Jin's plan during that game as well.
You may have come here looking for the answer of the connection between Kazumi and Akuma and I might just have it. We know the conversation between the two takes place some time ago. We're talking before the First Rave War some time ago. So this would have to be during Akuma's travels to master the Satsui no Hado but before Akuma incapacities Gouken. This would also link up with Kazumi being the first to carry the Devil Gene. Which could also mean that the Devil Gene and the Satsui no Hado may be connected in some meaningful way that predates either of their interactions with it. This would also explain why Kazumi could get Akuma to not only listen but also grant her request now that she's back in the picture. We do also know that Akuma isn't as monstrous as he portrays himself to be. For all we know is Kazumi could be somebody from Akuma's past and we know how he gets about the ladies in his life so his wanting to take out Heihachi could be more for his own personal reasons than even we know about at the moment.
One way or the other by time somebody gets some Fated Retribution is we'll know all. Or at least I hope so.
I've seen how divisive the streets have been on this subject so some parting words about that are in order I feel.
Just enjoy the crossover for what it is!
Be grateful we live in a world where the crossovers you talked about on the playground and in the lunchroom are possible and happening every day!
And always remember, be thankful not for the contents of the glass but be thankful for the glass that can hold the contents!
Until next time!
-Triple Da G.O.D!