There aren't any concrete plans for a sequel to Tatsunoko vs. Capcom yet (but it's Capcom, so there will be a sequel), but producer Ryota Niitsuma has some ideas about one, as revealed in an interview with Siliconera. Asked whether a followup game would appear on the Wii or HD consoles, he said "As the way I'm seeing it now, the sequels will be on the Wii as well."
He actually had some nice, fan-friendly reasoning for the declaration, different from his earlier statement about technical issues keeping the series on Wii. "If people are going to invest in this game, like we want them to," he said, "they're going to go out and buy arcade sticks. It would be a disservice to fans to just put out this one game that they buy sticks for and then they have nothing more to play."
Niitsuma also spoke a little more about the absence of Hakushon Daimao and the plan to replace him with "around three to four, maybe more" and the difficulty of designing online games for Wii.