The reference paper goes as far as to conclude that "hardware-based bot prevention techniques such as CAPTCHA tokens will become increasingly prevalent" and never touches on how this would effect players, just bots.
This is a a mighty bold assumption that ignores human behavior... human nature is to take the path of least resistance, so given a choice between a game that uses captcha and a similar one that doesn't, one can reasonably assume the game that doesn't use captcha is going to be more popular.
As a 15+ year old paper, it's conclusion and some of it's theory has basically already been disproven.

Enough on the paper, here is my thoughts on the article:

As a fairly large investor in Splinterlands, my vote will always be no to captcha.
Captcha is a horrible, frustrating tool that bots can deal with and I'm positive it would drive more people away than it would sedate the hate of bots.

Option 1 adds too much time to a game, most people could have found an opponent, and set/submit a team before the average person is going to find the lore.
Option 2 is complex (remember that a large percentage of the existing players doesn't use English as their primary language) and what about desktop users?
Option 3... buy some physical cards so I can trade my virtual ones... really?!?!
Option 4, well... first question is, how do you determine who is a bot in the first place? Don't say, well if they play all day, they are a bot, bots can and will run on a human schedule if the game starts targeting them. Think about it this way, if you can think of a way a bot could slip past detection, it will be done.
Option 5 has lots of assumptions.

The core problem is the draining of value from the game which you outlined well, I just don't believe that captcha is going to solve it and is a huge detraction.

The Splinterlands team has done well in the past to make adjustments away from being bot friendly, and I trust them to make future changes at a controlled rate. Remember, everything they do to slow down bots effects actual players as well.
The game is going to change a lot this year, so let's see what the team can do with bots before we even think about the ugly options.