Usually reaching milestones is part of the journey. Rarely milestones are deviations from the game's progress or rewards from an independent decision.
A good number of players don't use flint tools / weapons (because it has the same value as bone tools / weapons). In the same way, not a few are those who despise copper in favor of bronze.
Demanding 25 flint lances or 25 copper knives (as a milestone) would be a way to convince them to explore the entire technological tree. The same thing can be done with bronze swords.
________________

I'm playing the scenaro with a limit of 25 villagers. I like small villages and I find it fantastic. Thank you very much for the creation.

Maybe some combos that would make players go out of their way to achieve, like:
Kill x amount of each of the animals that become extinct, which they'd have to do before the extinction.
Surpluses of not so attainable or desired resources at the same time, eg. 100 fish, 100 fruit, 100 nuts, 100 bread which they'd def need to play differently to accomplish. No necessarily those numbers, but something possible without being naturally progressive.
Housing that would alter the usual way a player would upgrade, eg. 40 tents, 40 huts, 40 roundhouses as most players would be upgrading way before 40 normally.
Have 10 stables, 50 sheep and 50 cows at once, doable but a challenge as you'd also need a LOT of straw/grain.

Just some ideas.

Thank you for your answers. Milestones as part of the journey. Yes. + they give 2 points. The copper tools idea sound nice at first, but overall it looks like WOW. Kill 10 pigs. Super! Next quest: Bring me the tusks of 5 pigs And ahh yes, kill 10 scorpions.... Auaaaah.

I also skip most of the copper stuff :D

It's a nice idea but not so awesome.
The one with the fruits and nuts is also not so original :-(
The killing of Animals that extinct is already in the northlands or ancient warriors :-/