..... No inside knowledge, but I think Disney *might* be hoping to launch Harmonious July 4th, as a last minute special event to kick off the summer...
My logic:
1 -- No announcement but aggressive current work. If the plan was definitely October 1st, why not announce it with the Rat opening date? I'll suspect that they are hoping for July 4th, but don't want to announce in case they fall behind, in case there are more Covid spikes, etc.
2 -- Epcot's Flower and Garden Festival ends July 5th. With no Festival, with half the park under demolition, it won't be easy drawing people to Epcot over the summer. So launching Harmonious on July 4th would be a "magical" finale to the Garden Festival, while a great kick-off to Epcot summer. It would draw night time crowds to Epcot all summer.
3 -- Again, they are aggressively testing Harmonious now. What's the real time frame it takes to test and launch?? It was supposed to launch last Spring/Summer, and none of the barges had even launched prior to the Covid closure. So if it was just a couple months away when Covid closed the parks in March... and now they are actually launching and testing barges, I have to imagine it will be "ready" within the next 2-3 months.. and July 4th in 3 and a half months away..
So basically... at a minimum.... I think they are reserving decision and considering launching Harmonious July 4th.
And imagine if they really did it as a last-minute surprise -- It would garner them tons of positive Disney-media coverage to launch the summer.