How realistic are elephants going rampage all the time?

[ziegenpeter]

would be nice to add some kind of modifier when charging certain units from the front ... maybe +100 defense so the cav charge will be wiped out and routed.

Thats not what we were talking about, I guess. Horses WOULD'NT charge into a polearms formation, they'd try to turn away before. That should be included. Of course because of the sheer mass, some of these miserable ponies would get pushed into the pikes nevertheless