Ladies and gentlemen, gather around! Grandson of the illustrious John Gamefreak, and son to Johnathan Gamefreak Jr.: John Gamefreak III Esq. here. I've brought with me some leaks! I will also be fielding your questions to the best of my ability.

>New Alolan forms?
Yes - but they are all Johto mons, as many of you might have guessed (given GS coming to the eShop). They are a follows:

-Bug/Fighting Ledian (Has boxing gloves)
-Water/Poison Wooper and Quagsire (They look like they're melting)
-Fighting Aipom (not much about it is different except its red and has a fist instead of an open hand)
-Steel/Water Qwilfish (Looks like an naval mine)
-Ground/Rock Slugma and Magcargo (They're black with rocks in them kind of like asphalt)
-Dark/Ice Delibird (Looks like a Japanese burglar)
-Electric Mantine (Looks like an angrier Mantine with yellow on it)
-Grass/Fairy Bellossom (Has a more tropical motif, flowers, colours, etc)
-Dark/Psychic Girafarig (The tail faces the same way as the head and is larger/more menacing looking)
-Water Pineco and Forretress (They look like coral reef/anemone things)

>What is the "alternate story"?
Gladion escapes with Nebby and Type Null. It is also kind of implied to be a sequel at some points. For example: Lillie works alongside Lusamine. Their lab appears to be legitimate now, Lillie citing a change of heart after a "long needed trip". Gladion seems to think otherwise, hence stealing Nebby. No more Skull. New badguy team.

>Are there still island challenges?
Nope. There are gyms this time around. Actually, a big part of it is how you and your rival are the first to take on the gym challenge.