While Windows PC gamers have been diving head first into the newest Serious Sam since November, console gamers have just had to sit and watch. Don't fret though, developer Croteam has announced via Facebook that they do still intend on releasing the game to consoles.
Regarding Xbox 360 SS 3, it is in development, so we are on it since PC was released... It does require time to do all kinds of optimizations, first to fit all in memory and to get decent framarate, as 360 is rather old hardware now (512MB RAM, lower range graphics card etc). Of course, this is hardly a confirmed release date, but moving forward, developers and fans alike can remain hopeful the game meets that window. In the meantime, if you're looking for the overwhelming odds, hefty weaponry, and general sense of chaos the series is known for, you could check out the first two games of the series, Serious Sam HD: The First Encounter and https://www.trueachievements.com/Serious-Sam-HD-TSE-xbo....htm on XBLA.
Please be patient for around 4 more months for 360, we are doing our best to finish it in that timeframe.