1) Any and all PlayStation Characters could and should be available for DLC, you could even do one character DLC for (for easiness) $3 or a five pack for $10 (but they would be what they want you to have.
2) DLC levels. I'm thinking Racoon city DLC, MGS1 Shadow Moses base, MGS2 platform, Final Fantasy Airship battle ground, there could be endless battle stages.
Think, $3 for Chris Redfield, $3 for Jill, $3 for Leon, $3 for Clair, and $5 for Racoon City, as separate items or bundle them all for $12.
The list can go on and on. As long as the game is good and bugs are fixed this game will be around for a long, long time.
What DLC or DLC packs would you like to see?