possible yes
feasible, no
tl;dr at the end
in theory you could recycle a lot of fields ( with a LOT of work ) and omit a few others ( again, with a lot of work ) to make space in the flevel for those 'bonus dungeon' maps
then, someone would have to design these maps first. making a map from scratch is absurd work. I'm not sure anyone has even done it because so far all the maps are basically reworks of existing ones so they didn't have to make the entire walkmesh, scripting and god knows what else. And of course you need to do those. For every map. I'm actually not sure how the over-head camera is designed to work in the script code, so thats something you need to figure out.
and then obviously, new enemies, which all need models made, AI made and so on. And then there is the limitation of space in the kernel, where you would likely have to omit some items to make space for new ones. And there is the same problem but much more severe with the weapon and armors, too.
tl;dr: it's too much work for anyone or even any small team. Maybe when QGears is complete. Some day.
