You can post anything you want, but obviously 99% of the SteemIt population is interested in SteemIt, while any other topic is a bit of a crapshoot (although some others seem to rise to the top easily).

This will change as tags (substreemits?) get more strongly defined or the site matures in general.

But even as it is right now, next time you want to write a Medium post, why not post on SteemIt instead? On Medium there is virtually no chance of a direct financial reward if it takes off. There's some chance on SteemIt, so it's worth choosing one over the other.