Cave Story's 3D revamp comes to eShop on October 4 | Joystiq
Nicalis also swears this is totally the last time they re-release this game, this is the totally final, ultimate, definitive version - now in 3D with pixels rather than polygons. This version is really just the PC version of Cave Story + from Steam, but its nice 3DS seems to get the PC updates even if there's a wait.
Though in this case they won't be upgrading you from the DSi Version, so you gotta pay. The DSi version will be delisted come October 4th so this can take its place however if you already own the DSi Ware version, you'll still have access to redownloading that version - you just won't be able to buy it after.
So if the 3DS, Wii, PC and Steam versions aren't an option for you and DSi actually is, you might want to jump on that before its delisted.