Pokemon-go – Are Generation 1 Pokémon still able to hatch from eggs if they have a Generation 2 preevolution

Silph Road reported in their Study #6, published 2016/12/29, that regional Pokemon are no longer available from eggs. The study examined over 1600 eggs. It also includes a quote from John Hanke, Niantic's founder and CEO, saying that even when they were available, the eggs could be found only within their regions.

Not really, no. The only Pokemon that would be considered to be 'only hatched from an egg' are the region-restricted Pokemon. But, even then, if you were to travel to one of those countries, you could of course catch those as well. The region-restricted Pokemon can be seen here: What are the regional Pokemon?

Edit: I feel it is important to add that this is still a pretty hotly debated fact. There was a survey done which claims to conclude that out of approximately 40,000 hatched eggs, none of the Pokemon were region-locked Pokemon. However, there are some people who claim (with evidence) that they have hatched region locked Pokemon. Some of these people even claim to have spoken to the person who created the aforementioned survey, only to have that person dismiss their claims as lies or 'hacking'.

So, right now, I am leaning towards that it IS possible to hatch region-locked Pokemon, however, there is yet to be 100% conclusive evidence either way. You can see some of the threads on Reddit where users have made claims for both sides.

Edit 2: Just to be clear, the answer to the actual question at hand here still appears to be no, the edit above is just some additional information, some of which may be a bit beyond the scope of this question.