That'd be pretty sweet! And, of course Isaac would be having one of the most diverse movesets in Brawl. Sure, he won't be breaking the rules like Palutena (who has 12 original moves), but his Smash moves can still be varied drastically so that they aren't merely like Mario's Fireball, where you have the standard, the defensive, and the powerful-yet-slow variant.
Also, sorta dumb observation, but since today is Friday, we saw the last update for the week. There are 15 business days before Super Smash Bros. 3DS is released in Japan on September 13th, after which point it would behoove Sakurai to focus all the daily updates on the Wii U version since the game would officially be available and thus details would be online anyway.
That's... not a lot of time for updates, which means that we won't be getting just "Here's a shot of the game" type of images anymore. We'll be getting concrete details, and even if the Wii U still gets at least 5 mentions, at least 2 or 3 will be Assist Trophy-related, which'll work for the 3DS.
I still think Isaac is in this game, but since he's not a big name, he might be part of the final character debut trailer, which'll be a conglomerate of other characters, which'll probably include Shulk, Medusa, and/or King K. Rool, that'll roll through some of their moves before moving on to the next newcomer before ending with a final series of footage to help sell the 3DS version. Granted, it won't be as exciting to see a "Here's The Other Guys..." kind of trailer which'll just feature standard 3D shots of them followed by brief gameplay as opposed to a devoted Isaac trailer, but at least it's better than nothing.
'Course, when this happens, I expect a certain portion of the fanbase to ignite in a heated uproar that'll get hotter than the sun. But, they should've done their homework.