Making clue caskets untradeable wouldn't make the game worse, clues would be seen more like a minigame rather than fast money(selling) or a black-hole(buying) for them. The future is more than 450 days to come and so far they are like the duel arena most of the time you lose big money buying or gain a little if super lucky. Most people tend to sell caskets rather than open them. Paying 5-7m for an elite casket with such chances seem a bit ridiculous and plebs are getting rich for the few minutes of work which also looks kinda out of balance.
Since the day Clue scrolls were release there's only 1 druidic wreath that was received on 1st clue reward and 1 cloak spawned for Christmas event, I believe 10 people opening 10 caskets each have better chances than 1 person opening 100 caskets. because most caskets are being opened by one or two people, everyone is fighting over dye shards and we don't really see the rarest rewards so much.
I don't see how it would make the game better though.
If 1 person opens 100 caskets a day now, it shows that those 9 other players in your example aren't intrested in doing it. They are there for the money you make by selling caskets, not time you waste by doing money by opening the caskets.
I don't think the people supplying caskets right now are going to continue doing clues to open them, probably just moving onto the next best moneymaking method which would be nex.
The update in my mind would only benefit rich people who are hoarding clue rewards at the moment because they are cheap, buying druidic parts cheaply and then making caskets untradeable and the prices would go up alot.
Also the "plebs" as you mentioned, would lose their ability to make wealth but top % of rich people who hoard clue rewards would make bank off it. Doesn't seem fair to me. Seems to me that rich people are sick of getting druidic rewards in the game, so they want to stop it and then have the few super rares for themselves.