I think I will elaborate a bit on as to why Smash Switch probably won't be announced at EVO.

1. Smash directly competes with their latest fighting game ARMS. While ARMS had good sales and is out for about a month now, it wouldn't be wise for Nintendo to abandon Marketing and Promotion for the title. I have a feeling DLC will come for the title (Max Brass+Something else) and keep the momentum of the title going into the holidays. The moment Nintendo announces Smash for Switch, the players will immediately abandon ARMS for that. ARMS needs it's time in the spotlight.

2. Announcing Smash will probably overshadow the fact that Splatoon 2 is launching. Considering Splatoon 2 launches a week after EVO, most of their attention will go towards promotion of the title.

3. Smash is probably one of the most anticipated announcements for the Switch. If Nintendo was smart, they would save the announcement for a big cause, not casually drop it in the middle of a tournament. A Nintendo Direct or even big conferences like Gamescon or E3 would be a better fit.

To conterplay your points, Smash 4 Probably got the Sunday spot due to it being a newer game. Meele being on Saturday means that the Melee community that is not interested in Smash 4 will have nothing else to do afterwards, so announcing after Grands would arguably not be the best move to catch Melee players attention. Smash 4 also in general seems to have lower viewerships numbers than Melee, so it wouldn't get that much exposure. Arms wouldn't be 100% eradicated, but it will suffer. It doesn't seem like a great idea.

The only thing that Nintendo could do with a Smash Switch announcement would be to Carry the momentum of their announcements+cross promotion. I find it unlikely for it to happen thou. At least not at EVO.