Pokemon Go may be getting Leafeon and Glaceon in the near future as Chrales, a data miner, posted their findings in the latest batch of file scouring. The conclusion came after files referencing mossy and glacial lure modules popped up.
According to Chrales' data mining , there will be three types of new lures coming to Pokemon GO but ETA is currently unknown. What is known, however, is that the new lures are Mossy, Glacial and Magnetic and they can cause some Pokemon to evolve.
Chrales' post itself revealed the flavour text for the three lure modules and each of them can evolve a Pokemon. Considering Eevee's evolutions, Glaceon and Leafeon, are Ice and Grass-type Pokemon, respectively, it is only logical that Eevee will evolve into one of them when a proper lure is used.
In Pokemon mainline media, Eevee would only evolve into Glaceon when it levelled up near an Ice rock or into Leafeon if the levelling happened next to a Moss rock. Niantic's introduction of the themed lures will likely serve as a walkaround for the mechanic.
Meanwhile, the Magnetic lure will probably evolve Magneton into Magnezone in a similar way, but everyone just loves Eevee and wants to see its evolutions instead.
The same tweet contained some incomplete info about Raid Weeks in 2019 where possible research tasks were to win a raid on easy mode or win a given number of them on medium or hard mode. Considering the tasks list "Win (?) raids" as an objective for the latter two, it is highly possible players will be introduced to a bit of grind with the new content.
Bear in mind that data mining has not been officially confirmed as correct by Niantic just yet, so it would be wise to take the new info with a grain of salt. On the other hand, Chrales already has a history of correctly leaking future Pokemon Go content which brings some credibility to the news.