The extending is a nice feature, but after third time it slows things down to much for my personal taste.
Perhaps add every time it extends more fallspeed to the blocks.
Or an extra, when you make a “Vetris”, which shrinks the playfield again.
Let random timed some Triangular shaped physic blocks “rain/fall down”, which are blocking some positions, but delete them after 3 minutes, when they die, they remove surrounding blocks, (similar) like the bombfunction in multiplayertetris on NDS.