It's not like RE is short of the insanity allowing for variety in enemy types a-la X-COM.
Funny enough, certain types of enemies in RE6 actually work a lot like/are based on the same concept as Xcom's. Yeah, that could be an interesting side project. Farm it out to a prestigious western PC dev and let them have fun with it.
If people want to hear what I would like to see done: (fan fiction time)
1) REmake 2. Maybe aim for a lower budget and release it on everything like they did Revelations.
2) RE7. Next gen. Keep it big. Carry over RE6 mechanics and make refinements based on what worked and what didn't. This means a highly detailed, but optional tutorial at the very least. Three campaigns + other content.
a) Two "solo" campaigns, but with a twist. The quickest way to describe it would be what if Leon and Claire scenarios from RE2 could be played at the same time by two people. Either through system link or players being dropped in and out randomly online, these two characters will inhabit the same open-world/hub area. How of it is a co-op game depends on the players. Additionally, players can drop in as monsters in these open-world area, similar to Agent Hunt (maybe include Hunk as well). Aside from this, there will be instances where players will have to go solo (sort of like overworld -> dungeons transitions you see in other games). If I had to pick these characters it would be Jill and Claire, with the former being on a mission and the latter being more a civilian looking for someone (a daughter? husband? the husband should be unimportant, anyway). One idea is to have the first part of one of these campaigns consist of a heavily wounded character who moves slower (with the game being designed around this), i.e. making a chunk of one of these campaigns (at least in the solo instances) play more like RE4/5.
b) In this open-world/hub there could be "side quests", but instead of fodder, they should entirely be a means to access multiplayer content. Additional modes like Survivors, Predator, and Onslaught should be turned into these quests.
c) A third campaign being RE5/RE6 style co-op, working much the same way. This would be separated for the most part, but likely have cross-overs like in RE6 with the other two at some point. Instead of taking place in one large area, it would be the usual world-trotting adventure (ideally with a visit to a gothic castle). If I had to choose this would be Jake and Sherry.
d) Raid Mode would be turned into a pseudo-campaign(designed to be played a hundred times over, with harder and harder modes), probably named "The Raiders". 4-5 big ass maps (inspired by RE:R's Ghost Ship stage) with somewhat randomized enemies, objectives, and mega bosses (these should act and feel like enemies from Monster Hunter) to be played by four+ BSAA agents, drawing from a cast including Chris, Rebecca, Sheva, Quint, etc (each having their own unique weapons/skills/upgrade paths). Less progression elements and certainly less power creep. I see leveling up characters to get new abilities (skill trees) and loot that degrades over time, but can be repaired by sacrificing loot. Loot can also be gained from doing side-quests in two of the campaigns. I'm thinking more Monster Hunter than Diablo.
e) The Mercenaries. Not much to change here. Shouldn't be at all affected by loot or whatever. Keep it pure. Maybe make it slightly more deadly? More unique enemies?
f) Focus on maintaining the Mercenaries and Raid Mode content in the future. Maybe even make a F2P version of Mercs/Raid at some point. Make a splash everytime you make a major update. Dino Crisis stage/dinosaur enemies with Regina. RE1 mansion with Wesker. Dead Rising mall with Frank West. DMC1 Dante... Akuma (based on the old EGM joke)... go nuts, make that paper. Have there be both Raid and Mercs version of each new map.
What not to do no matter what: Make another game like Revelations. RE6 was an awesome action game. Revelations was a mediocre one at best and didn't do anything special to make up for it.