Subdomains do make it a little clearer for users which part of the site they're on (apart from breadcrumbs). For example, compare:
With Google, you won't see any advantage in SEO with one over the other as of late. See this for more about that: Subdomains vs. subdirectories for SEO: No SERP benefits for ...
I guess it depends on the content of the site, if it was an adult site you might want to include the transgender options.
But don't transgender people identify themselves as either male or female? Why not leave it at that...or if that isn't enough, put "other" which often puts a smile on someone's face.
If ad revenue used to work, but isn't anymore, and you don't want to charge visitors an access fee, then the next most typical model is to sell the user data to someone interested in your user's demographics. But that would assume that you have some (probably somewhat private) information about your users.
Other ways that are less tested, but possible ...
If this is not a SaaS you can prob do it like so: Make sure the community app folder is named "community" and lives inside the folder that your TLD is pointing to. Goto mysite.com/community and see if it works. If it doesn't, change the configs/settings in the community app to use the new URL scheme. Once its all linked and loaded, make a 301 redirect to ...
OpenAtrium is based on Drupal and for free. The default organizational unit there is a group. It provides a blog and a notebook (wiki) and some features for each group. It took me about 1h to install and configure and I have seen some nice themes for it as well (but not yet tested).