In anticipation of TheouAegis' CV3 engine, I put together a little bit work on a design document for just such a project as this. I call it "Castlevania II: Dracula's Curse". (It may seem to be an odd choice of title, but it's close to the original Japanese Title of CV2 in meaning & my remake of CV3 would be titled "Castlevania III: Legend of the Demon Castle".)
Anyway, my idea for the game was to have the player start in the Town of Jova during the day. The player would be able to buy some items at the town's shop and then exit either to the left or right of the town. The two paths never cross like in RoB and here's where your gimmick comes in. Whichever path you choose the stages making up that path will progress from morning to sunset until you reach the Town of Doina. You will be told at Doina that you must have all of Dracula's parts before you enter Dracula's Castle. Now you proceed back to Jova where it is now night and the place is crawling with monsters and you are forced to take the opposite path from the one you took before. The stages in the second path progress from night to sunrise back at Doina where you are now allowed access to Castlevania which is itself expanded into a set of four stages.
This Day/Night gimmick is different from that in the original version of CV2, but I think it keeps to the original spirit of that mechanic. Furthermore, it extends play time in a way that isn't tedious by giving you a different experience on a second play through by choosing the pathes in the opposite order from before.
I should also, like to mention that on the second path, being that it takes place at night, none of the towns have shops available like on the first path.
Here's the basic stage progression I came up with:
Start
Jova (Day)
Route A
Belasco Marsh
Dead River 1
Brams Mansion
Dead River 2
Aldra
Sadam Woods
Strigoi Cemetery
Ondol
Dead River 3
Jam Wasteland
Deborah Cliff
Route B
South Bridge
Veros Woods
Berkeley Mansion
Dabi's Path
Aljiba
Yuba Lake
Rover Mansion
Joma Marsh
Laruba Mansion
Debious Woods
Uta Lower Road
Cross Paths
Bathory Mansion (Both Deborah Cliff & Uta Lower Road lead here)
Wicked Ditch
Doina
North Bridge
Dora Woods
If Your Reach Dora Woods at Sunset
East Bridge
Denis Marsh
Jova (Night)
If You Reach Dora Woods at Sunrise
Yomi
Vlad Graveyard
West Bridge
Castlevania Ruins (Here a cut scene showing Simon burning Dracula's parts happens & the Dracula Wraith is summoned.)
Castlevania Wraith
Entrance + Chapel
Outer Wall + Underground & Courtyard
Cursed Dungeon & Laboratory + Clock Tower
Castle Keep
This short version of Castlevania is loosely based on the NES/MSX version, but in barely stable ruins. I was thinking of trying one of two things to represent the chaotic, half-formed nature of this quasi-revived version of the castle. A) Super-Ghouls-'n'-Ghosts-style shifting terrain effect during game play, or... B) Semi-randomly generated 'chaos' rooms dispersed within each stage.
That's pretty much my idea for a linear CV2 remake. Of course many of the areas will have to be completely redesigned to make things more interesting, but that pretty much goes without saying.