I tried to compile all the information we have thus far because as time goes on people are just trying to spread nonsense, and the OP isn't being updated. I left out completely unreliable/unaccountable stuff (4Chan, Discord), but all of this stuff shouldn't be taken as fact and people should use their own judgment.
Information:
Early testing for MvC4 will begin next year
Source: YogaFlame24 via Twitter
MvC4 will be announced at Playstation Experience/Capcom Cup, a 2017 Title
Source: Names withheld to protect them, but established members of the FGC/
Ryce say it will be announced specifically after Capcom Cup Grand Finals.
Source: Polygon's independent sources point to an announcement more generally this weekend.
Source: Eurogamer's own sources corroborate an announcement more generally at the Playstation Experience.
Source: SneakersSO says we'll see it at the PSX keynote first.
Mentions this repeatedly, as well as that what will happen at Capcom Cup will instead
be an exhibition.
Source: Lupinko.
Source: shinobi602
Team Ninja is involved
Source: Names withheld to protect them, but established members of the FGC/Ryce.
No more X-Men, focus on MCU Characters
Source: Polygon suggests, with the author clarifying on twitter this conclusion was reached by what
he was told to expect.
Source: Eurogamer corroborating Polygon's claims.
Source: Nibel via Twitter.
Source: A Malaysian animator via d3v of SRK, although
d3v later said not to put too much stock into this as the source could not be confirmed
MvC4 will feature Ant-Man & Groot
Source: Polygon, with the author
specifying that these characters were specifically named.
Source: Eurogamer corroborating Polygon's report
MvC4 will feature Dr. Strange
Source: Eurogamer.
"Good news for fans of Marvel vs. Capcom 3 specifically coming soon"
Source: Polygon
Speculation: A UMvC3 port to be announced at either the TGAs or PSX based on a
sudden UMvC3 stream by Iron Galaxy, and
Marvel-Related tweets by Iron Galaxy CEO, a developer that has a history in doing Capcom re-releases.
MCU Film Actors involved, there is no "4" in the game title
Source: Nibel via Twitter.
MvC4 is a Sony Exclusive
Source: SneakersSO heard about a year and a half ago that Sony made a deal with Capcom to develop a Vs. game, later
specified as Marvel from
sources close to Capcom.
Combofiend is the new battle director
Source: sephi22
Will be more casual-focused compared to SFV which is more competitive-focused, have big marketing push
Source: sephi22
The Gameplay will take a 2v2 + 1 Assist Format
Source: A Malaysian animator via d3v of SRK,, although
d3v later said not to put too much stock into this as the source could not be confirmed.
Teases/Ambiguous/Probably Nothing:
Lupinko tweeting about X-Men
Source: A post-Polygon article
beserker barrage of X-Men related tweets,
some of which have #datmarvel.
"Bounce"
Source: A series of GAF posts by bishoptl:
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