1) What type of Shard do you think Astaroth will have and how it will be?
I sense something like a blast or fire shot or dark energy wave.
2) What type of Shard do you think Mafeius will have and how it will be?
Dark energy or dark feather shot.
3) What type of Shard do you think the boss Gremori will have and how it will be?
That one I thought about early. Crescent moon blades or some moonlight power (maybe to be buffed up temporarily)
4) What type of Shard do you think the cameo enemy Shovel Armor will have and how it will be?
He will be a mini-boss but will help later on, probably as a familiar. I hope he won't end as a NPC or quest-giver. It's sad that he likely won't be playable (the story would hardly fit him anyway).
5) From what kind of enemy do you think the magic Gluttony Summon will come from and what type of Shard it will be?
Maybe a legion of ghosts... (yeah, it's going to be cliché). The pic shows it... they will get thrown at enemies and cause damage, maybe status ailments.
6) From what kind of enemy do you think the magic Magical Throne will come from and what type of Shard it will be?
Either a poltergeist or tskumogami or just one soul waiting for Miriam to save. Will it help with HP recovery?
7) From what kind of enemy do you think the magic Winestained will come from and what type of Shard it will be?
Maybe a wine drinker, heh. Make it like the holy water of lore.
8) The magic Voltic Chain was described as a special “seventh" ability—not a demonic one. What do you think that mean? If it comes from a shard, what kind of enemy and type of shard would it be? If not, how Miriam will obtain this magic?
What are chains about? Restraining. I feel it's linked to liberation and distance attacks, something different from a whip, maybe to compensate the lack of range of some weapons.
9) The Clan Katana has won the votes and that made the Katana one of the most powerful weapons in the game. How do you think this powerful katana will be obtained? By forging? By finding in the game?
By finding a raw, disappointed version of it, then by forging and embuing, it will be one of the best weapons around.
10) The secret IGA BOSS will not look like it's concept art (it's just placeholder) and we know it will give a Swordwhip as a prize. Do you believe it will also give a Shard? What type and how it would be?
A swordwhip would be enough (as well as a bestiary entry and an achievement). Him as a familiar would be so fun too, but I doubt it will ever happen.
11) How the Armor Familiar will work out overall in the game?
He hopefully will be an extension of Miriam. I admit I was truly disappointed with familiars from the past igavanias. I want them to have their own set of commands with a move and some input, maybe triggered by the shoulder buttons, with MP and cooldown. I don't want ones that float around and hazily hit when they feel like to.
12) Do you believe the Swordwhip that will come as a prize for backer-edition ($60+) will be overpowered or underpowered? Do you believe the game will give other players a way to forge it or find it?
Oh trust me, it will be overpowered, but gotten late and maybe you'll have to work on it. Why pledge if it's to get some disappointing content?
DLC? It's not excluded. That said, backer-exclusive content would not disappoint me since I backed the game.
13) Aello doesn't seem to give any shard at the E3 2017 Demo. Do you think Aello is a Lesser Demon, like Morte (and thus, doesn't have any shard) or Aello does have a Shard? If do you think it does, what type of shard it is and how it would be?
"Did not seem" doesn't means she doesn't drop one. Let's find out when we get a new playable version of the game.
Razor-sharp feathers or summoning Aello for a diagonal swoop seem plausible.
Enjoy!