My question has to do with usability, because, believe it or not, some of my experience is in making command-line programs more useable. That's part of it. The other part are things you can't do in the current screen UI, that you can do on the command line. For example you can just start MAME and run a game. You don't need the command line at all for that, but to get HLSL sliders to save you need to do some initial configuration setup. That is something that might be put in the UI somehow.
My point is that complaining about general ideas, esp. ones some people are really, really fond of, like the command line, is a waste of time because it doesn't tell us what you really want. It's like going to a car dealership and complaining because you can't drive. You should be specific about your complaints. What are the specific scenarios that give you grievance?
Let me approach this from a different point-of-view. What about the emulation of old computers? If you want to play Ultima or Wizardry with the Apple II emulator, are you going to complain about having to use that command line? You can, but it'd be fruitless. You will have to use the command line to get those games running. Playing certain games will require a certain knowledge of the system they run on. Likewise, using MAME requires a certain knowledge of the CLI. It's very basic knowledge that I believe anyone who can read can learn. Devs can do their best to make things as accessible and simple as possible by providing good docs and up-to-date information, but at the end of the day there is a minimum amount of computer knowledge you'll need to have in order to use stock MAME.