I am not a fan of mythos, canon, lore etc. I am a fan of making mythos with the players at the table. Listening to other players mythos is like listening to them describe their sex lives; the stories are lot better to remember than to listen to. This also applies to large corporate shared mythos that can literally rake in millions of dollars. To use the sexuality analogy, corporate mythos is porn. All extremities aside there are several really good reasons to separate mechanics from mythos
Mechanics are the tools that allow the players to have a mutual experience with the mythos they create. Mechanics ensure that a lazer pistol does lazer pistol things in all the plot points of the evolving story. A lazer hurts the target persona, opens the lock on the door, and bounces of reflex armour. Without this shared mechanic the experience moves (devolves) from a table top game to pure story telling. If the table wants a lazer pistol that makes personas fall in love then their personas have to build it themselves. This is creating their own mythos. If you are not building your mythos you are a revenue source.
Now pure mechanics is not good enough. I have learned this over the years. Few of us have the creative fortitude to play a table top game off of pure mechanics. There will always be cross pollution. Think of it as a separation of state and church. One is the rule system the other is the fantasy.
EXP is building a generic mythos that easily allows players to slip their own words into the fantasy. The delusional fantasy is that the generic mythos appendix in EXP will become a parody of wikipedia.org called wikexpedia.org