I found your post brilliant, but why do you think that DOA won't enjoy a new pool of players in spite of this whole new context? A lot of non Xbox players are actually willing to step back into the ring to compete.
To be clear, DOA5 will definitely have a new pool of players playing the game.
Having new people playing the game, and having new people who are willing to support are tournament scene are not the same thing.
I don't think anyone doubts there will be new people playing when DOA5 drops. Casual players will likely flock to DOA5. Most of the players of any given fighting game are the casual players. However casual players do not hold tournaments. There may be a huge influx of people who are willing to play the game online and have online tournaments, but there is a decisive difference between online and offline tournaments.
The offline tournament experience is simply better. It's not just a matter of playing the game without lag, which is reason alone to attend. People who are willing to travel to show up to events are all obviously very passionate about the game. In addition, people offline are for the most part, pretty cool in person. All of the online bravado is gone and replaced with something more genuine and legit. On top of that they can be very helpful. Clearly there are exceptions but when you go to offline tourneys and play people, you stand to learn a lot more than you could just by playing online. But online vs offline is a different topic entirely.
DBZ Budokai 2 had a lots and lots of players. But there wasn't any tournament scene because they were all casual players. Whether or not a tournament scene exists won't make the casual players any difference. Most of the changes you hear the competitive players asking for won't make much of a difference for most casual players either, because they don't explore the engine that deeply. However it makes all the difference in the world to the competitive players.
You said that the Tekken community has never been amputated, but actually that's not true. A lot of the people who played TTT competitively stopped playing when Tekken 4 came out. The removal of characters, the new throw system, the nerfing of backdashing and sidestepping, awkward slopes, the emphasis on jabs, and the unfairness of the JFLS made a lot of Tag era players quit.
Lots of us found ourselves playing Soul Calibur II instead. To be fair Tekken 4 on it's own merit is a great game. It was just a poor follow-up to Tekken Tag Tournament, and it's new mechanics alienated a lot of veterans. Many Tekken players lost interest during T4 and didn't come back until T5 and T5DR was released. Were there new players to T4? Absolutely. Enough that it still had a good tournament scene. But compared to the Tag era? No where near as many people playing. T4 lost more competitive players than DOA ever had.
The reason why T4 was able to manage during it's loss of players was because a lot of people who had been throwing tournaments beforehand continued to host tournaments. DOA doesn't have a lot of players who do that. I mentioned early about competitive players wanting to bring in other competitive players? Part of this is because competitive players will host tourneys for games that are popular enough, regardless of whether or not they can play them well. The term fighting game community is tossed around a lot, but it's a community because we usually hold tournaments for more than one game. And for a long time now, DOA hasn't graced monthlies or majors on any sort of regular basis.
Having new players is a given for DOA5. Having new players who are willing to host and attend tournaments is not.
Ideally a casual player who is confident in their skill will decide to attend a tourney. They go to a site such as Freestepdodge and see a tournament coming up. Maybe they feel up to traveling a good distance, or perhaps they happen to be local. They go to the tourney, they have fun, they improve their game, AND they get an idea of how to host tournaments themselves. They host their own tournament, and thus the cycle continues. However this doesn't happen when no one is holding tournaments. Casuals, despite all their charm don't hold tournaments. At best they have gatherings with a few friends. This is why a new influx of casual players doesn't seem promising to competitive players.