I think if we want a 4x4 baja we are going to have to make one ourselfs.
Now that BL power is avaible I think it will be much easier to do.
If HPI does make a 4x4 baja if will favor the gas version use belts to get power tot eh front.
There is a "knock off" company that makes a 4x4 baja and it uses belt drive to power the front wheels. You can find it on ebay.
http://cgi.ebay.com/1-5-Scale-Gas-Po...item255eceb30b