Well, considering it was ported based on 360 sales, I can say it did pretty well. Not the perfect Castlevania by any means, but the potential is still there. I also heard from some IGN report that Harmony of Despair was among the top 20 downloaded on the PSN since its release, so I suppose that should mean something for it. I can't say that another online castlevania game 100% will be released in the future, but it has a shot. Konami need only fix a few things gameplay wise, then it possibly could rake in more sales and respect from the gaming community that likes action/platformers.
My thoughts on those fixes in the spoiler :P
Hmm, I've enjoyed my time with Harmony of Despair, and even today Im still playing that game almost every night. I'd definitely jump for another Castlevania online game, but as others have mentioned there's a few things that need to be fixed:
1) Rebalancing:
both in effectiveness and content since Soma pretty much is favored for the game. Give the whip users more martial arts and sub-weapons, give Alucard more dark spells and let him use more of his forms, give Shanoa more glyphs to gather, give Maria and Yoko more variety. Something to help even out the playing field with Soma. Course in respect to that, we should get more stronger enemies/bosses to fight.
2) additional stages:
now the DLC was nice but the game has much more potential to expand into the various maps we all know, but could also come up with original stage designs to keep things fresh. As many have pointed out, the copy-paste method is lazy, still castlevania but lazy nonetheless.
3) additional characters:
For any sequel, more characters are required to show how much better it can be. I find that the gameplay is more important than the representation, but both do need to play their parts well for it. For as long as we can see more characters with varied gameplay that would be good (especially if they were made specifically for the game or characters that haven't stepped into the 2d plane yet).
4) enhancing the single player experience:
The appeal of playing with many other people is great, but there are times when you can't find people to play with. Some sort of a story mode, perhaps unlocking some characters, or even just making things easier for single players to farm for certain items would be great. Harmony of Despair suffers from this issue, it's meant to be played online with others, but it's single player is seriously lacking (it's only use really is for spell farming, since everything else would be easier to get online).
5) other aspects:
The timer doesn't bother me too much, but it would be nice to remove so people can actually enjoy running the stage at their pace (instead of them rushing to the boss and ultimately their death). The drop rates could be raised a little, or make it easier to get those rare items (also not as big an issue for me personally). though if that were to be done, the content would need to be increased to lengthen the game properly instead of the artificial length due to farming. A traditional leveling up system might do good, but for characters like Soma that would make them more OP. Rebalacing will come into play again, but the traditional leveling up I wouldn't mind having at all. Least then Johnathan won't take a century to level to max, and all the characters can be paced easily.
... yeah, that's all I got ;D Probably is a lot to ask, but who knows. Sonic team learned with Generations, perhaps Konami might get a clue on what the fans want and still manage to reel in new players.