question about summoning in lore

[Enkidoh]

Actually, Earth does have a connection to several FF titles, if at least tangententaly, although those are spinoffs (and two are not games but animated features) - FF Tactics Advance's 'St Ivalice' is obviously a contemporary Earth city somewhere, presumedly Europe/the UK judging by the architecture, and FF Unlimited started in then contemporary Japan (with the JSDF torn apart by Bahamut!)... and then there's FF The Spirits Within set in a post-apocalyptic Earth (and mostly in New York). FFVII also was meant to be on Earth in New York in an early draft of it's story (with those discarded ideas recycled for FFTSW).

As for 'calling' someone from Earth to Hydaelyn/the Source, it could theoretically be done, but, it appears that to call summon from across the Rift from another world is extremely difficult and dangerous - when Elidibus hijacked G'raha's call spell and started summoning other Shards' WoLs in ShB at random, he wasn't fully summoning them but merely pulling their spirits across (effectively killing them in their home worlds).

And even the Azem crystal seems to only work on those we've met or journyed with in the past, it doesn't seem to just pull in some random adventurer who happened to be sitting on the privy at the time. And although the Azem crystal did seem to work across the Shards or even on the other side of the Universe, again it only works on those we know - it doesn't seem to have the power to just randomly pull in average Japanese high school student #28654 from his bedroom. And yes, characters from other worlds, both FF and non-FF have been appearing in crossover events, as Cleretic mentioned, so the possibility is there.

Breaking the Fourth Wall though, in some respects, maybe you yourself have been already summoned to Hydaelyn in a manner of speaking? (In the form of your character, when you login to the game). The game has teased that possibility a few times in a tongue-firmly-in-cheek manner, but that mind-bending idea still persists.... "Heed the Crystal's Call" indeed....

*Pulls out darksteel foil hat again*