No

That only works with the gzdoom source port because it can do more complicated stuff

it's impossible (with our current limits) because in order to at least run custom wads you would need a full on dos emulator and with how this runs doom it can't just throw in the dos emulator app and call it a day because you can't so it would need a web code based emulator that works as a full OS and then you would need to run the dos emulator in it which would need to be in a code the OS emulator can understand and blah blah blah so the simple answer is NO (at least for now i hope)