Welcome views on this.
The proposal would be restricted to certain armies from India and South-East Asia that maintained large stables of elephants. It would not be available to other armies (such as Hellenistic armies). Yes I know Ptolemy Keraunos was supposed to have been killed when on an elephant, but you could restrict that to scenario games.
Basically this would be identified in the list notes as a special rule. It would permit generals in the army to be mounted on elephants. When not attached to UGs, they would be restricted to moving at elephant move distances. It would permit them to fight in elephant TuGs, adding +1 (even if a legendary general).
Richard