I was thinking abouta simple improvement - allowing heroes to use behemoths instead of their own ships. I always thought that not allowing heroes to use biggest ships in the game is kind of stupid, a general should use one of the major vessels in his fleet due to the simple safety. They wouldn't even need to boost any of behemoth's stats that much, just allow them to use this ships for safety. 

Additionally, it wouldn't be a bad idea to use heroes to enchance the production of support behemoths (some of their skills could be altered to also boost certain modules).