I do hope they go all the way to IV. I'm one of these weird guys who actually liked it. It's balance issues do get annoying in a hotseat, but it has the best story of all HoMM games (save the expansions, which 3DO imposed on NWC as they figured no-one cared anymore. I cared. And I got disappointed...). There's a fan made campaign for HoMM 5 that continues the story of the originals and it was quite a surprise to me. I just hopped that Ubisoft would make it part of the same universe but another world (if you know the story since the Might and Magic RPGs, you'll know that this is quite possible).
Also, I'd love if they brought us the Might and Magic RPGs as well. 1 and 2 may be nearly unplayable nowdays (unless they give mouse support and other few tweaks), but 3 to 5 are nearly unplayable for other reasons (DOS-box is really a nuisance to use).