And a dual E3 reveal is vastly unlikely since they actually intend to stretch this out among 2 years, not 5 for 1 year(and it was closer to 6 for 1 year, since PP was part of the same year as the other 5) when it came to release and work d one on it. It was just luckily revealed in December, if I remember right. So less than a month before the next year. Also keep in mind they started working on it at least by September, so it was able to release early within the next year. Imagine if it wasn't like that. They'd have to have spread it out significantly more cause 6 characters in one year wasn't really plausible overall. Considering Hero had balance issues, Banjo was way more simplistic than anyone else, and we still had more than enough glitches as is... it's no surprise they spread out it among 2 years for the next pass. They had to delay two characters, and we still had some issues with Steve. They've been taking their time... for a reason).
They have no good reason to do so. It doesn't give them time to really show off content that well. Realistically, we were getting at most one E3 reveal last year anyway(which was Min Min, if anyone), because there was other times to reveal characters. She was already taking long enough to be put there as is, and the gameplay was an easy reason she was delayed. Steve could've no way have been revealed with her either, as they needed a lot of time to redo every single stage. It would've been a later reveal anyway, and it made sense to delay it a bit(if any) for Minecon. Min Min is literally the only announcement where we had to wait for any information. The rest were significantly faster for the presentation. They clearly aren't spreading out the reveal proper and presentation much at all(and even with the Min Min thing, that was for a different reason, namely that they were trying to get ARMS back into the market, which barely worked at all, so it wasn't a very good idea in the end) now. I expect a single reveal at E3, and one in the Fall later on. With no clear delays, they don't have anything off-schedule, so there's no real reason to worry about factors like this.
Banjo frankly is a poor example, since they were doing 6 presentations in a single year. They had to group at least one set together to make it on-time. Remember they only had One Pass entirely, and it was meant to be done in the year. If no other Pass was going to happen, they could've easily stretched out over the next year too, by changing up the times. Banjo as DLC, honestly, is more of an exception to how DLC has been going for Ultimate. Nobody else was a dual reveal, but they literally has no reason to do so beyond one year anyway. It also helps that PP's reveal was earlier than Joker's(and Joker's was a last minute reveal), showing things already went off-schedule.