I actually think they will milk SFV for YEARS considering how well it's doing in the e-sports scene. I also won't be surprised at all if they slowly release the game on other platforms and given how successful the Switch is thus far (as well as doing very well with UE4 games), I think it might be the first one. All this of course depends on negotiating a deal with Sony.
I don't feel like this is likely, to be honest. Companies are extremely reticent to say anything concrete about exclusivity but with SFV Capcom has been pretty clear that Street Fighter V won't ever appear a non-Sony console. Maybe Sony signed something like a 5 year exclusivity period or a "current gen" exclusivity period but it seems more like that SFV is stuck on Sony systems for good.
I feel like if SFV is going to go to anything else it's going to be in the arcade or the PS5 if that isn't fully backwards compatible with the PS4 from the get go.
Depending on when the new gen of consoles come up, I predict we might see a new SF by either 2021 or 2022.
I figure we'll get another PS3/360 length of time with the current gen because they're already doing incremental upgrades. Plus, if SFV goes the distance with Capcom's plan and is still pumping out seasons in 2020 then they'll need at least a year or so off before SF6 so people don't get burn out. That is if Capcom learned their lesson with SF4 because casuals won't be interested in a sequel to a game that's only stopped getting updates like a year ago.
I won't deny that tons of casual content is a big part of why NRS is successful but they're also smart enough to not keep updating their games for years and years. They do MK for a few years and then switch off with Injustice for a few years to keep the casual audience enticed. Now, I would hate if Capcom took that approach with their games because I love playing the same games for years but the NRS method seems to help launch sales tremendously.
