Read what MegaByte posted and you'd see there's fishy stuff going on.
At this point, I'd say there's still two possibilities: Either this is all viral marketing for a new Blaster Master title, potentially a retro one, or it's viral marketing for the original found game. Either way, the eBay auction clearly isn't coincidental, and is meant to drive up buzz about whatever Sunsoft has coming up. Considering the press release, I'd say there has to be something on the way, likely for the 4/26/10 date, like Sunsoft said, or they'd probably be in legal trouble, as well.
So, I'd say either Sunsoft made the game in the past year, they found it, or they always had it unreleased, a la EarthBound 0, and given the success of Blaster Master on the Wii and in general, they figured they'd release it. To drive up buzz, they made the announcement on April 1st, then had an unbelievable auction go up simultaneously, after some negotiations with a relatively known arcade collector. All these things together scream April Fools joke or viral marketing, two things that can go hand in hand. Considering the possible legal issues of making an announcement about an item that doesn't exist, the game was announced today as part of the viral marketing, rather than as a joke.
So essentially, I think something is happening with Blaster Master, and it's happening soon, but there's no real way to tell what it will be, at least not yet.