With the announcement of MG Char's Gelgoog as MG No. 99, Bandai really got everyone guessing who No. 100 is going to be. I read from Gunota Headlines that Bandai will even give away exclusive gold plated MG No. 100 to fans who makes the right guess. Too bad it's not an online competition, since the participation form (in this case, postcard) are available in some affiliated Japanese magazines, namely Gundam Ace, Dengeki Hobby Magazine, and Hobby Japan.
For those who live in Japan, I'm sure you'll be anticipating for the magazines to get those postcards, as much as I'm to see who's No. 100.
My guess is ZZ Gundam Ver. 2.0. Wanna bet? :-)