interesting idea, how are people manipulating their hands?

The GU land allows you to Scry at the cost of card advantage. There's things like that Cephalid you noticed earlier. Mostly, the faction simply hopes to have a good range of Dignity creatures on the board, and can be expected to alter their hand size by maybe 2 in either direction on a given turn. The neat thing about it is that many of these creatures want your hand to be the right size at different times, allowing you to benefit from the effects of things of multiple CMCs each turn.

sorry i didn't reply earlier

i think this ability is probably too clever by half. it means you're constantly playing this involved hand manipulation subgame, and playing that game often involves playing cards/not playing cards at times where it would otherwise be optimal to do the opposite

threshold (Krosan Beast)is an ability that's been widely derided (i personally quite liked it) for the subgame reasons, and it wasn't as fiddly as dignity is; everything triggered at 7. but graveyards are a lot more linear than hands; they typically only go up where hands can go all over the place

basically i don't think hand size is a great variable to be using for ability word triggers. it's too variable and controlling it isn't much fun

I will admit that this card is a very poor Dignity design; it's always sad to have it as the only 2-drop in your opening hand.