Hmm, so there was some buzz in the fighting game as Harada Tekken x Street Fighter was dead. Turns out there was an error in translation. Some nuance in the meaning and intent of "okura-iri" was lost, which meant "shelved" or "in storage" in this instance.
https://www.vg247.com/2021/06/22/tekken-x-street-fighter-not-dead/
He was saying they got about 30% finished, but it has been put on hold. So there's still hope.
I'd love for it to happen, as I think 3D fighters have mostly done a better job of bringing 2D fighters and other guest characters, than 2D fighters have done(apart from Smash, if we're counting that.)
Soul Calibur VI has 2B from Nier, Geralt from Witcher, and Haohmaru from Samurai Showdown.
Tekken 7 has Akuma, Geese, Noctis from FFXV, and Negan from Walking Dead.
Dead or Alive 6 has Mai and Kula from King of Fighters. Several Virtua Fighter characters too, although VF is much easier to translate to DOA.
They've all worked out really well, with two of those games being Namco properties. And they've even ported Street Fighters characters already, so they've shown they can do it. I'd love to see it come to fruition, especially if they avoid the pitfalls of Street Fighter x Tekken.