Steam is the name of an extremely successful and long standing game engine, games made using this engine are often referred to as 'Steam Powered'.
The similarity struck me the first time I heard of steem/steemit.
steem.engine or any similar variation/derivative would likely raise issues, I think steem & Steam are close enough as it is, which takes steem engine off the list.
Every single time I tell someone about Steem, they immediately ask, "Isn't that a gaming platform?" Almost every time I google something about Steem, it autocorrects to Steam. I think this name collision is just going to cause more headaches later on, and it might be better to change the name while the platform is still young.
I like your name by the way. I did not know this about the game Steam. Thanks for the information.