The only unconfirmed pokemon i can see Ash getting so far is the fire monkey (Boappu) and the Grass/Fighting legendary (that's right, a legendary for Ash)
The writers obviously will want to showcase the three monkeys in a triple battle due to the blatant synergy they have with each other (Why else would Gamefreak create three pokemon that 1) look identical asthetically, 2) share the same type triangle as the starters, and 3) are featured in a scenario in which the first gym leader will own the one that has a type advantage against your own starter). Dento is already confirmed to have Yanappu, the grass monkey, which leaves Ash and Iris with the fire and water monkeys. Since Ash is already confirmed to have another water type (Mijumaru), he will get Boappu, leaving Iris with Hiyappu, the water monkey. Besides, the fire monkey is a perfect fit for someone like Ash, who has just spent the past three years taming a certain other fire monkey (coughblazeapecough).
As for the Legendary, I believe that, after featuring a legendary user in a pokemon league with virtually no backstory, there is nothing holding back the writers from having Ash capture one for himself. The Grass/Fighting one would work out well in terms of preventing the majority of the fanbase from viewing Ash as a cheap uber abuser in the same way they view Takuto for two major reasons.
1) It is clearly a member of a trio, with the other two members being the Rock/Fighting and Steel/Fighting legendaries that are listed before it in the pokedex. As such, it is still subordinate to a greater authority (which would be one of the more powerful legendaries), which means they wouldn't be able to hold a diety-esque status. In addition, a future league rival could capture the rock or steel fighter, which creates an easy backstory for the writers to work with. Another option is to build up its connection to Ash in a similar manner to Ash's connection to Azelf, having Ash catch the pokemon during the aftermath of the Team Plasma Climax.
2)Grass and Fighting together perfectly symbolize Ash's personal style: A Down-to-Earth, ambitious trainer who never backs down, and fights to become stronger through natural, humane means. The majority of Ash's out-of-the-box strategies involve utilizing one of the five senses, synonomus with nature, and in turn, the grass element. Ash also tends to deploy his pokemon in melee battling positions, rather than hit-and-run, ranging positions, with is synonomus with the fighting element.
Those are my two cents
