Scarlet said day 4 will be quite eventful but it is also said that characters are being introduced and the milf arc "takes shape in the next week or two". Although I'm pretty unsure whether the weeks mention irl dev time or in-game story time is.
I'd be pretty much happy if the update is going to be as big as you paint it to be but I'm saying this again: Unless the dev comes around and announces the next update to be particularly big, be it by animations, scenes or word-wise, I would refrain from stirring up expectations which might just backfire.
The only thing being big in this case is the reveal of new characters. I'm happy and very interested to see scarlet's work and vision coming to fruition. There are various teases in the post of what might happen but as long as nothing concrete is being said I would simply wait. Scarlet delivered in most cases 'good' updates by providing quality animations, well-written text and a good chunk of content in general.
Yeah high expectations will just kill the experience for you and hurt the game in the long run. The update will definitely be a morning update so I'm not expecting anything too crazy but the dev always has something fun to show in his game so I'm not worried.
It seems some of the new characters have been shown in futa on futa or hidden as random npcs in the past. For example the f*cking THICK waitress from day 3. Lord have mercy she's 2x THICKER than Hana.