If Magento choses to use it (To me it seems Magento 2 tries to get as far from dropdown as possible) then a way how module developers can also use it should be well documented not like drop-down list creation now.
Magento 2 module Royal Mail Shipping where the list of radio buttons is quite big for customer to look through would need that.
Also Estonian post offices dropdown menus added to shipping method that are in more difficulty to create in Magento 2 (Maybe that is the reason why Estonia does not have any commercial shops that uses Magento 2.x) then they were in magento 1.x pages, but they are necessary because no one would scan through such amount of radio buttons.
The way described in those posts can solved both problems (city and state drop-down and shipping methods).
As it is well known most of the orders that are made in ecommerce websites comes from mobile devices and as mentioned articles referred dropdown lists are not user friendly.
Hopefully shipping-methods block extension would get finally documentation for long list of items.
CAN ANYONE SEE A REASON WHY MAGENTO SHOULD NOT USE SOLUTION FROM THOSE ARTICLES?!