Sure, and no CAFOs (which is somewhat a given/necessary if you're not abusing antibiotics). So grass-and-algae-fed beef in regions where growing crops for human consumption is not very viable, because not everything grows everywhere and because humans (unlike cattle) do not have 4 stomachs with which to process plants that are not particularly nutritious.

Additionally, are you implying that anyone is suggesting beef should be the primary food source for 10B people? Because I've never seen anyone make that claim. You didn't say "how about we reduce meat ag and use something more scalable for feeding most people", which is a stance I agree with. Instead, you said "how about eliminating meat ag altogether", which is what I was replying to.