Here are my thoughts for each of the Galar Pokemon we've seen and their evolution lines. This is mostly just based off my gut, but some of it probably will be true.
Grookey: It's a starter. It's going to evolve two more times. 'Nuff said.
Scorbunny: See Above.
Sobble: See Above.
Wooloo: It's going to evolve once more and gain another type, probably fairy or steel.
Gossifleur/Eldegoss: That's it. Nothing much.
Drednaw: It's going to evolve one more time, and keep its typing. Just looks like a first-stager to me.
Corviknight: Regional bird, has a pre-evolution with the same type combo.
Yamper: It's going to evolve once, keeping its pure electric-typing.
Impidimp: It's going to evolve two more times and look really cool but ugly in the final stage. Final stage also is different type combo
Alcremie: Not going to evolve. Just a gimmicky single-stage Pokemon.
Rolycoly: Evolves two more times. Sort of the Geodude/Roggenrola of the Galar region. Final stage will be a tanky Rock/Steel (or possibly Rock/Fire) "meh" thing that people remember, but no one puts it on their team.
Duralodon: Druddigon situation. Stuck as that stupid thing forever.
G-Zigzagoon/G-Linoone/Obstagoon: No more evolving.
Morpeko: Single stage pikaclone.
Cramorant: Evolves from a really weak bird thing found mid-game. Doesn't evolve further.
Polteageist: Middle of a 3-stage line. Evolution gains a type and a lot of weight/size.
Sirfetch'd: Won't evolve further.
Derpy Fish that Cramorant spits out: A hardy 3-stage water/dark-type fish/eel found in several water areas in the region.
Squirrel silhouette: 2-stage according to the leak.
Chairman Rose's Pokemon: I only saw two frames of this thing. Not guessing yet.
Weird dark spiky things at docks: Final of three stages of a weird-looking evolution line. Can gigantamax.
Zacian: Can't evolve, but can gigantamax.
Zamazenta: Same as Zacian.
We'll see soon how many out of 21 I got correct.
Edit: Forgot to do this earlier, but here's how I did.
- Grookey/Scorbunny/Sobble: I was right, but that's not saying much
- Wooloo: Does evolve once, but stays normal. Half right
- Drednaw: I was very wrong
- Corviknight: Was the regional bird at least, so I'm counting this one as predicted
- Yamper: I was very right
- Impidimp: Besides the type, I was right
- Alcremie: Doesn't evolve, but has a prevo so I was wrong
- Rolycoly: I was very right on this one
- Duralodon: Again, surprisingly correct
- G-Zigzagoon: I was correct, but that's not surprising
- Morpeko: Ding! Correct
- Cramorant: Ehnn! Incorrect
- Polteageist: Sadly incorrect
- Sirfetch'd: Sadly correct
- Derpy fish (Arrokuda): I was definitely wrong
- Squirrel sillhouette (Skwovet): I was right
- Weird dark spiky things: Don't know what they were
- Zacian/Zamazenta: Incorrect
12/21, or 4/7, or about 57.12% correct. I guess I did kind of well.