Perhaps he meets a new trainer. If he wakes up in a different region, there could be a trainer passing by who is intrigued by Ash's strange appearance or situation. This trainer could either be helpful or see Ash as some sort of oddity to be captured or studied.
He might meet Pikachu first. Since Pikachu is his closest and most loyal Pokemon friend, it would be likely that Pikachu would be by his side when he wakes up. Pikachu could be really confused at first but still show concern for Ash in his new state.
It could be a wild Pokemon. Maybe he wakes up in a forest and the first thing he sees is a curious Pidgey or a mischievous Meowth. This would set the tone for his new adventure as a Pokemon or in a Pokemon - like state, having to interact with the local Pokemon population right from the start.
He might meet a mysterious old wizard. The wizard could be the one who brought Ash to the room, either for a purpose or by accident. The wizard could then guide Ash on a journey, or perhaps be an antagonist who has some dark plan for Ash.
He might meet an old Pokémon expert who gives him tips on hatching the egg.
He might meet new Pokémon trainers in Alola. Maybe some young kids who are just starting their own Pokémon journey.
Team Rocket is the most likely candidate. They've always been after Ash's Pikachu and tying him up would be a way to stop him from protecting his Pokémon. They could use ropes or some kind of Pokémon - powered restraining device.
There might be a young and inexperienced trainer who is lost. Ash, being the more experienced one, decides to help the trainer find their way. This new character could look up to Ash and in the process, Ash learns more about himself as a role model. It would be an interesting dynamic as Ash is usually the one being guided by his friends.
In this kind of fanfiction, Ash might wake up with new Pokemon - like abilities. For example, he could communicate with Pokemon in a more direct and profound way, like understanding their every thought and emotion just by looking at them. He might also find himself physically changed, perhaps having some physical features of a Pokemon, which could lead to all sorts of interesting adventures and interactions with his friends and other Pokemon trainers.
Ash might meet a strict teacher who has no idea about Pokémon at first but gradually becomes interested in them. He could also meet a rival in school who challenges him not only in academics but also in Pokémon battles.
His friends like Misty and Brock would probably visit him.
Maybe it's a legendary Pokemon in disguise. In some fanfictions, legendary Pokemon often play important roles. It could give Ash the egg as a test or because it senses that Ash has a pure heart. Another possibility is that it could be a young trainer who can't take care of the egg anymore and trusts Ash to do a good job.
He might meet some of his old friends again, like Brock or Misty. Maybe they will join him on his new journey through the regions.