Can we make afk farming punishable please?

Afkfarming is already punishable and it's actually detected by the systems as well most times. However, there is a difference between afkfarming and simply split pushing to try and pressure/win.

AFK farming is absolutely NOT detected by any system. Otherwise Nasus mains would be crying foul in unison with KKkHHHAANNNNN!!!!!! Show me a ban where someone got AUTOMATICALLY banned for AFK farming and I'll sell you a desert island, off the coast of Australia, with 64 virgin women, all skinny, with a height of 5 feet 11 inches, weight of 95 pounds-105 pounds, and all the fine wine to last you 100 years. Now if you combine it with intentional feeding and cussing and flaming, then yes.

Depends on your definition of "AFK Farming" If you're talking about an adc hitting a side lane to come back from behind then nothing will detect that because it's a common tactic. If you're talking someone legitimately sitting in a side lane and waiting for the wave to push to them then farming until it pushes out then sitting still until it comes back then yeah. Systems do detect AFK.

It already is.

Though it is typically a manual review thing.

I've never been punished for AFK Farming and I do it all the time (NOT every game obviously but often enough, since SOME champions MUST afk farm), and I have over 2000 games played.