.

You wouldn't have this IRL when playing a game...

While it's true that it's not a part of the game IRL, I think it's something that would really improve the game offline as well! Plus I think it's very easy to make such an implementation yourself IRL by just placing a piece of paper on the finished tiles! So with that in mind it might be best to have it as an option! :)

It's true that this isn't a feature of the real-life game. But in my opinion, correctly reading which cards are part of finished groups is not really the "point" of the strategy in this game. Or, saying it from the other direction, if a player accidentally thinks that a finished group is unfinished, or thinks that an unfinished group is finished, (to me) that's a genuine mistake, not bad strategy. If my opponent made a mistake like that in real life, I would say, "Ah, I'm sorry that that happened, I wish we could go back and fix it," not "Haha! I am a better player than you!" So (in my opinion), the game would be easier to play, and not any less interesting, with this feature.

It would be ideal if this feature was an option that could be turned on or off at table creation. That way, people who want it could use it, and anyone who feels like it is a significant difference from the paper game could turn it off.

Yes please !

(The debate between IRL and online play is pointless. It's not the same so why try to mimic it ?)