I've argued for and against a challenge system. It has merit but it does still also have it's flaws.
I'm not wanting to get into days long debate but I have raised the point before that this isn't necessarily a good thing, from a referee perspective anyway.
It rarely happens but let's say Joe Blogs challenges a referees decision. Fine. Ref plods to the monitor. Disagrees with coach. Decision is final. Cue whole footballing world in meltdown once more... What about they agree, but the rest of the world doesn't. Same again. Referees at the centre of controversy once more for, as is some times the case, the correct call.
We've still got that same problem we're craving to fix as far as I can see. Ultimately I feel it's worth a trial, but I dont think we'll be able to measure it's true success until it is used in a live elite environment. And be good to test whether the benefits for outweigh the negatives.