yes, that’s possible, but that would mean multiple locations to manage your domains (i.e. - manage the domain in htaccess, manage the domain in each individual index.php, etc)
a couple years ago when I was on the Xoops dev team, I created a Multi-Sites mod (which Mithrandir continued after I left). a single code-base was used for each site, the sites were served up based on the requested domain. had a configuration file for each site, and i modified the addon modules so that you could choose a specific "Site ID" for each piece of content (or you could leave it at the overall selection so that the piece of content would be available across all sites). additionally, if you wanted, you could references all content across all sites if you wanted, since it’s accessible in the DB
I don’t believe I had to work up any special htaccess rules for that, just PHP/SQL. worked well for me, but that was then and this is now