First time I think he made a mistake. The second time, judging from the smiley he used, he's going along with his previous mistake for comedy.
I'm gonna assume that otherwise I'm gonna go crazy trying to think how I could word it without making it confusing.
Anyway, 7 more characters would work very nicely as you could fit most all the fan favorites and most expected. If I had to wager a guess/wish list I would say...
Newcomers
Shantae: Likely and wanted by me
Geno: Likely and I'd be interested in
Isaac: Likely
Echos
Ken: Don't really like but seems incredibly likely
Shadow: Basically the same as Ken
Dixie: Likely and my second most wanted after Shantae
And last Medusa(if 7) Or Medusa and Viridi(if 8)
Now I know a lot of people would be upset with Kid Icarus getting two more echos, but here is my reasoning. In Smash 4 Palutena had 12 unique special moves as her main gimmick was that her custom moves were completely different from her defaults rather than being variations.
Now in Ultimate, it looks like custom move just aren't a thing anymore. Which means there are 8 unique special moves going completely to waste. I don't see Sakurai wanting to let all that work go in vain, So I definitely see him making one echo to use 4 of them and could just as easily see him making another echo to use the remaining 4.
Medusa and Viridi both have a staff/polearm weapon so not much about them would need to change. And yes, Viridi is shorter than Palutena, but Young Link was a clone of Link back in Melee even tho he was shorter, so I don't see that stopping them.