Maybe we get 150 new Pokemon for Sun/Moon like Red/Blue . Don't forget that so many thing refer to Gen 1 . For example MeleMele(Yellow) island = Pokemon Yellow (with Electric Guardian Legendary) . The 3 other island refer to Pokemon Red,Blue,Greem (with Fire,Water,Grass Guardian Pokemon)This is possible list by far we can confirm by ourself

1. Rowlet
2. (2nd evolve of Rowlet)
3. (3rd evolve of Rowlet)
4. Litten
5. (2nd evolve of Litten)
6. (3rd evolve of Litten)
7. Popplio
8. (2nd evolve of Popplio)
9. (3rd evolve of Popplio)
10. Rockruff
11. (Rockruff 2nd evolve) I'm sure Rockruff evolve once
12. Komala
13. (Komala 2nd evolve) (all of bear evolve once just like Teddiursa,Cubchoo,Panchum)
14. Pikipek
15. (2nd evolve Pikipek)
16. (3rd evolve Pikipek)
17. Yungoos
18. (2nd evolve of Yungoos)
19. Grubbin
20. Charjabug
21. Vikavolt
22. (Dragon + Kid)
23. (Dragon + Daddy)
24. Drampa (Dragon + Grandpa)
25. (pre evolve of Bruxish)
26. Bruxish
27. Cutiefly
28. (2nd evolve of Cutiefly) (just llike flabebe)
29. (3rd evolve of Cutiefly) (just llike flabebe)
30. Togedemaru
31. Salandid
32. (2nd evolve of Salandid) (main Villain Team Pokemon always evolve once like Sharpedo,Camel,Drapion)
33. Pre - evolve of Bewear (all of bear evolve once just like Teddiursa,Cubchoo,Panchum)
34. Bewear
35. Mimikyu
36. (2nd evolve of Mimikkyu) (just like Gengar,Chendelier line)
37. (3rd evolve of Mimikkyu)
38. Fossil A
39. Fossil A evolve
40. Fossil B
41. Fossil B evolve
42. Tapu Koko (Gaurdian of Yellow island aka MeleMele)
43. (Gaurdian of Red island )
44. (Gaurdian of Blue island )
45. (Gaurdian of Green island )
46. Solgaleo
47. Lunala
48. Mashadow
49. Magearna
50. Wimpod
51. 2nd evolve of Wimpod
52. Bounsweet
53. 2nd evolve of Bounsweet (just like Cherrim)
54. Comfey
55. 2nd evolve of Comfey (just llike flabebe)
56. 3rd evolve of Comfey (just llike flabebe)
57. Mudsdale
58. 2nd evolve of Mudsdale

more or less , and we still have 4 month before release date