I think I have a bit of a Romantic view of fandom, and so I lot of my thoughts are inherently biased by that point of view. Having said that, I want to say that I think we live in a "Period of Headcanons" right now, with the understanding that I'm using the phrase "period" relative to the time scale of the internet.

By that, I don't think there's necessarily been a major increase in the amount of headcanons available for consumption and viewing, but in prominence alongside media. I believe it's partially the result of more complex lore becoming increasingly a more common facet of mainstream media. I think there's probably a correlation between having more content and fans expanding more, or at least having a desire to expand and fill in the gaps left behind. From that, a headcanon emerges.

Headcanon tends to be, generally, sorted into two types. There's a 'filling' headcanon, which is an idea that connects or assumes in an area otherwise untouched, and an 'overlaid' headcanon, which is placed over an established part of the canon to superficially correct something. As stated before, I think there's a correlation between media having lore and the amount of headcanons, but specifically, I believe there's an increase in the 'overlaid' type of headcanon. This is partly the result of continued expansion in lore, which results in 'filling' suddenly being overtaken by canonical information. If that headcanon persists, it automatically becomes 'overlaid' by definition.

However, because headcanon tends to be specific to groups within a larger fandom, 'overlaid' ideas tend to be viewed as intentionally contradictory by 'outsiders' who lack the context necessary to fully understand that information. Since it is seen as intentionally contradictory, those who disagree with them or those who prefer another interpretation often think of that contradiction as aggressive rejection. Of course, not every 'overlaid' headcanon is the result of media outgrowing ideas. Sometimes those ideas are simply preferential, but that doesn't tend to make them viewed any better than the previous subcategory. In fact, that intentional contradiction tends to make them be viewed with even more hostility.

Going back to the idea that we live in a "Period of Headcanon" and connecting back to the ideas of 'overlaid' ideas on expanding lore and the resulting hostility, I think there's a 'current' of discourse that carries ideas further and spreads headcanons both to those who accept them and those who reject them, in turn spreading them further through discussion. That current makes more headcanons visible, making it seem like there is a higher density of them, with a generally larger online population and interacting that in previous years assuring that. More importantly, this 'current' which spreads headcanon through discourse creates a larger group consensus of the legitamacy, or illegitamacy, of these ideas. That increased legitamacy in the eyes of the larger fandom population places some headcanons on the same level as media-canon. Simply put, when enough people support a headcanon, it becomes as legitimate as official canon.

For these reasons, I believe that within the larger "Era of Fandom" we are in, we currently live in a "Period of Headcanon." This unofficial period is characterized by the prominence of fan-made ideas alongside media canon in online fandom, as well as the discourse that spreads these ideas to a larger population.