Worth to take fruit of grisaia now?

No chance of being bundled anytime soon given a theme for this type of games has already been done. Maybe at least 6 months - 1 year till next one or maybe even not anymore

Tbh it's a good deal for 7$. I doubt it will be bundled soon, or even discounted more.

Eh, I wouldn't recommand the anime myself, but yeah, Grisaia is totally worth its price, really nice visually, pretty lenghty and I can't think of any route that wasn't at least good, and yeah, I wouldn't expect it to get bundled soon

To be honest, even for such a low price, I wouldn't get it (or any of the main Grisaia games) from Steam... unless you like paying for incomplete products.
Every franchise that's been touched by Sekai Project has been horribly butchered with bad translations, and/or unneeded censorship (or outright missing content) -not only the obvious 18+ scenes- with no available patches, not to mention they're extremely aggressive towards fanmade ones.
Frontwing seems to have regained the rights to the Grisaia IP, but I'm not sure that'd actually be a good thing in the long run...

Firstly, it's censored (18+ scenes and side stories have been cut) with no patch available -there used to be one, but Sekai nuked it and it's not been rehosted anywhere else- so you'd need to buy the unrated version to get the full story, while the sequels (Labyrinth and Eden) have no patches at all, and likely nobody will ever bother.

As for the length (main games):

1. The Fruit of Grisaia - vndb very long (50+ hours) | HLTB ~20 hours main story, ~60 completionist
2. The Labyrinth of Grisaia - vndb medium (10-30 hours) | HLTB 8 hours main story, ~30 hours completionist
3. The Eden of Grisaia - vndb medium (10-30 hours)