Hitsuji Mamoru: Those are some pretty nice ideas. Houyi is a pretty likely candidate for Grand Archer, and I hope he shows up. More Knights of the Round Table is also good and Fiore seems like a pretty interesting Saber. I also imagine that Paris is going to be added to FGO whenever Achilles is put in the game. Also, maybe Lugh could be summoned through Bazett as a Pseudo-Servant.
Regarding Savers, I see them as very interesting and wish that there was more of them. Hopefully, Buddha will appear in Last Encore.
I don't mean Apocrypha's Jack. I am talking about the appearance changing one, who has already shown his skills and Noble Phantasms. Isn't he just a normal Berserker, who just can appear in many forms and has his Mad Enhancement being sealed. Do you mean that you want to see what will happen when the Mad Enhancement is unsealed?
Fillia also does seem pretty interesting.
Well, I would personally be interested in seeing more of the Third War Servants, most notably the twin Sabers probably. Seeing more of the Hassans would also be cool as we have only seen a couple (like 5) so far.
Also, strange fake's False Berserker has appeared quite a lot and we know a lot about him, so not sure why he is on the list.
Ah, okay. I'll take your word for it, since I'm not that knowledgeable about the Hindu Gods.
Although, it does seem that the anime might be altering parts of the story and changing things, so it might be structured differently from the game, just due to the differences in media forms. Nasu himself is also writing the anime so he could be more ready to later parts of his own story.
Quetzalcoatl is a somewhat special, as the Aztec Gods were famous for using mortal vessels. Due to this, an aspect of her has been summoned in the form of an unknown woman. Or something weird like that.
On Chiron, it would probably depend on how powerful the Greater Grail actually is. If it could actually fulfill any wish, then it should be possible, in some form at least. The interesting question then would be if there would still be a version of Chiron that is a Heroic Spirits and another that is a Divine Spirit. Or maybe the Grail would not have that power at all, as we haven't really seen the full extent of its abilities.
I apologize if I am simply unaware of something, but why wouldn't it work on Parvati or other powerful gods. I don't remember something like this being stated, although it could be real. But is Parvati really that strong? Again, I might be simply misinformed. but she doesn't seem supremely powerful when summoned as a Servant at least.
Although this is just speculation, Odin could probably be summoned as a Lancer, Rider of Caster. He would be pretty fun to see and as for his Noble Phantasms they would probably be Gungnir (his spear), Sleipnir (his horse), the knowledge gained from giving up his eye (as already pointed out) and summoning his crows, wolves or even all of the warriors of Valhalla. He would defineatly be powerful, as a leader of the Norse Pantheon, but I'm not sure he could overcome Gil. Maybe though :)