IGA is running out of material. Aside from remakes he's got:
1. The 1897 game. Which would be very nice, and go a long ways towards branching the storyline away from Bram Stoker.
2. The 1999 game. The grand finale. And something that should be handled with definate care.
IGA's got more ideas than that. He's already brought up the ides of:
1. 1999(as you said)
2. 1897(as you said)
3. Something taking place in betwee, LoI and CV3, where "the Belmonts were fighting "other" vampires. (Note: You can make a LOT of games taking place in THIS period since there's some centuries in between LoI and CV4).
4. Direct sequel to HoD(which follows Juste's adventures AFTER the events of HoD).
5. Direct Sequel to SotN(which follows Alucard's adventures AFTER the events of SotN).
6. The story of how the Belmonts lost the power to wield the whip and had to give it up to the Morris clan.(This can actually be put side-to-side with the SotN sequel, as both would take place around the same time).
Those were the ideas he's talked about in various interviews. Not to mention ideas of having a female Belmont starring in a modern-themed CV game, or even a Black Belmont(or vampire hunter) who was inspired by the Blade movies(IGA seemingly likes them).