I dunno. I must be the only one who feels the tune from that Gigant Battle 2 trailer comes nowhere close to the epicness of We Are! With voices singing to the melody, it may sound better, but all in all I'm getting a bad feeling from it. Sure, it has tons of motifs and recognizable sounds that I'd describe at One-Piecey in nature, but above and beyond it all I'd call those sounds a confused maelstrom of 'how many different instruments, sound effects and melodies can we squeeze into a short theme song'. It lacks cohesion. But, if anything, I feel it would have been a perfect fit for the One Piece 3D movie, which was 100% chaotic and free-spirited in nature.
But as a replacement/follow-up for We Are? Nope. It does not come close.
The animated stuff I saw in the vids looked pretty epic though. :)