If they just said "a trailer will be released this month" then this probably is the trailer.
Since July they've been doing a section called SMTV News. This one right here is the last one, from August.
Each one of those has been preceded by PV trailers, which so far have been the big ones. So far we got 3 PV trailers as Idon explained. First one was the E3 one, second one from July where a week later we got SMTV News Volume 1, then the third PV trailer in August with the second volume of SMTV News the following week.
In these SMTV News videos they basically expand and give us more info about things showed in the most recent PV trailer at the time.
We know the next SMTV News livestream is scheduled for late September, a detail they say at the end of the video I've just posted.
That's why I was saying I feel like the Direct is going to take place next week, among other reasons. We'll have the Nintendo Direct next week with the newest SMTV trailer (PV #4), and then the week after the trailer will get it's corresponding deep dive with another SMTV News livestream, which would happen during late September as they just informed us in August.
If my memory serves me right, Nintendo promoted the heck out of DQ11S before the Smash release of Hero. He came off from my POV as a bonafide shill pick because of how they were pushing 11S. Again doesn't really mean much for Nahobino besides that SMTV's promotion by Nintendo sort of mirrors DQ's.
They also promoted Monster Hunter: Rise a lot, and while it got Smash content... it wasn't a fighter.
And Monster Hunter is a big IP in Japan, just like Dragon Quest, and MH: Rise is a console exclusive unlike DQXIS, so if we just talk about promotion, Nintendo had more reason to add the Hunter from MH than the DQ Heroes.
What I mean is, yeah, SMTV being a Switch exclusive and being significantly marketed by both Atlus and Nintendo is definitely a good sign and not a point against a SMT character, but I literally remember some people here in January/February being quite convinced about the Hunter being CP9. And we know the end of that story.