The idea of limiting paragon to 2k is bad as it won't solve anything in my opinion. People would just farm to 2k and then stop farming xp and do other things which would effectively make the player-base smaller in a shorter period of time after season launch.
Captcha is also a bad idea because it's not "game-like". You are playing D3 to kill demons not to fill up some forms and answer stupid questions.
Regarding whether captcha can be solved by bots or not, it can be but it's not that much of a simple task. Also, there are certain types of captchas that cannot be solved by bots (yet) and those are usually a bit more complex than just typing in the wrong letter+number combination but again, it makes the game "un-gamy" so It sucks.
If captchas were implemented, anyone in my position would be forced out of the game. I have impaired vision and It is likely that I would be unable to identify obscured characters/digits/etc. This would seem unfair to me, as I have already purchased the game.
Very simple 3 digit captcha on opening a rift would end d3 botting overnight.
Never heard a counter argument to implementing this, only ever passive aggressive whining from leaderboard botters. I don't have anything against paragon grinding, d3 is about grinding. The problem is the botting not the system itself. Breaking the paragon system won't stop people from botting keys etc.
Only issue is that a LOT of streamers would quit if this came into place, and blizzard don't want that.
There would just be bots that open a game, bot the outer world, then remake the game.