One of the issues with the original Cities: Skylines is the way you unlock new public transportation options. The unlocks are based entirely on population milestones: you get access to taxis and buses when your population reaches 650 people, but cable cars, trains, trolleybuses, and monorails come later down the line when you have enough citizens to qualify as a Big Town and a Small City. That means you need thousands of residents before you can access those important services.
The problem is that well-designed cities are built around public transportation systems like trains and trams, and that works much better than building a city that supports thousands of residents and then trying to cram public transportation into an existing design. Lay the tracks before you build the skyscrapers, in other words.
That's why it's great news that in Cities: Skylines 2, new modes of public transportation won't be unlocked by population milestones. Instead, as we learned today in the new Cities: Skylines development diary, public transportation options are unlocked using something called "development points."
Unfortunately we don't know exactly how you earn development points—that's being saved for a future development diary. But we do know you'll be able to spend those points on the type of public transportation you want to unlock next. Buses and taxis will still unlock based on population growth, but after that, everything else will be unlocked by spending your development points, so the choice will be yours instead of being based on the size of your city.
That's a smart change. As the development diary says, the original milestone system "resulted in similarly built cities as each option was always unlocked at the same time, regardless of the player’s need to use them or not." In Cities: Skylines 2, if you want to focus your young city on using subways, ferries, streetcars, and presumably even airplanes (and hopefully blimps!) you'll be able to unlock them in the order you want and get access to the systems you need earlier than you would otherwise.
I think this is a great tweak to the formula, and I'm hopeful the development points system will extend to other parts of the game—public transportation isn't the only thing dictated by population milestones, but also unique buildings, different industries, and other services. The more decisions we get to make about when we get to access new services, the better.