I'm going to apologize ahead of time...cause this is gonna be a long post haha.
So here are the current known participants:
1. Rey Mysterio
2. Chris Jericho
3. Kofi Kingston
4. Randy Orton
5. Shelton Benjamin
6. Vladimir Kozlov
7. Big Show
8. Undertaker
9. HHH
This leaves (let's do the math kiddies) 21 superstars left.
We can rule out the champions and the challengers, obviously, so no Cena, Jeff Hardy, Edge, or JBL. We can rule out Batista as he's injured.
Some people are damn near guaranteed to be in it:
10. John Morrison
11. Finlay
12. MVP
13. CM Punk
14. The Miz
15. Tommy Dreamer
16. Chavo Guerrero
17. Santino Marella
18. Kane
19. Mark Henry
20. Cody Rhodes
21. Carlito
22. Khali
23. HBK (even though they said he wouldn't, c'mon. He has to be, due to the severely low number of upper midcard or main event faces in this match).
Some people are inactive and we can't be too sure if they'll be thrown in there. This includes Umaga, Mr. Kennedy, Evan Bourne, and Ted DiBiase.
Matt Hardy and Jack Swagger probably won't be in it as they'll most likely just be in the ECW title match.
The rest of the guys have the same shot as each other. Any of them could be thrown in as equally as the ones next to them, but chances are, they won't. This list is Paul Burchill, Charlie Haas, Kizarny, D-Lo Brown, DJ Gabriel, Val Venis, Ryan Braddock, Boogeyman, Gavin Spears, Cryme Tyme, Scotty Goldman, Bam Neely, Funaki, Jesse, Dolph Ziggler, Sim Snuka, Curt Hawkins, Zack Ryder, and Jimmy Wang Yang.
But here's the other grouping...people that are above that jobber list up there, but are still in jeopardy mainly due to whether or not any "legends/guest stars" show up and who (if any) of the inactive/injured return. This list is Gregory Helms, William Regal, Mike Knox, R-Truth, Manu, Festus, The Brian Kendrick, Ezekiel, Ricky Ortiz, and Primo Colon. Out of that list, I think the three with the best chances of being involved are Helms, Truth, and Kendrick, and the one with the least chance is Ezekiel, who will most likely just accompany Kendrick.
There's a good shot that they'll put Goldust in it, but I don't see them really bringing in any other former stars.
Out of that list, the Final Four is tough to call, but you can VERY safely narrow it down to 12 people: Jericho, Orton, Kozlov, Big Show, Undertaker, HHH, Morrison, MVP, Kane, HBK, Umaga, Mr. Kennedy.
Out of that list, you're going to need at least one face. You can't have a final four of all heels. Since Orton is the obvious favorite to win the whole thing, we can put him in there. The only faces out of that group are Taker, HHH, HBK, and Kennedy (who may not be in it). Here's where it gets tricky. Taker has no current storyline, but you can never count him out. HHH is almost a lock to be in the final four because, well, he's HHH, and he'll probably eliminate Kozlov as well. HBK is very confusing as they're saying right now that he's not in the Royal Rumble at all, but we know he'll be in it, except you also have to take into account that JBL could screw him out of it and I can't see that happening in the final four. It'll happen earlier than that.
SOOOOOO....my predictions for the final four: Orton, HHH, Undertaker, and either Jericho or Big Show. Final two coming down to Orton/HHH, with Orton winning, cause HHH will want to be in the final two again as that's 2nd best to not being able to win it.