I would at minimum like to play this with a Hold option. I'm not a huge fan of the mechanic in normal Tetris, because IMO dealing with and recovering from unfortunately-timed pieces is a key part of the game. But, that's not really an issue here!
Hold changes the game enough that if you don't like it I can't blame you, but it's not about recovering. It's about storing T pieces to allow B2B TSD to be performed safely, without the threat of 5-10 lines of garbage coming your way. In general, I fall on the side of those who like it because it opens the game to more variation in strategies. Removing hold would also be a buff to strategies that aren't particularly fun to play against like 4-wide.
But that's for PvP games. IMO, the problem with modern Tetris rules is that they're optimized for PvP modes at the expense of marathon mode.
In marathon mode, the only garbage blocks are the mess you create for yourself. These arise naturally from situations such as (1) receiving the wrong piece at the wrong time and (2) failing to maneuver a piece correctly before it locks. It is good for these situations to arise naturally during the course of the game.
If I was in charge of Tetris, I would retain Hold, EasySpin, and piece previews in PvP games where they make sense, but I'd disable them in marathon mode.
