It's been mentioned already, but I also wanna stress it: More pricey = okay, more RNG = please no
There's nothing inherently difficult about RNG, it's just pure frustration distilled into a game mechanic, since you won't know if the effort you just put needs to be repeated 10 more times, 1000 more times, or just one more time.
Two players putting in the same effort in the same strategies can have wildly different experiences, which can easily end up in bitterness on the less fortunate side.
Another tricky thing, and that's totally on gravity's side, is how jumpy item progression can be.
Peak example would be e.g. time dimension rune crowns, where for some builds they're borderline useless until Grade A at which point they suddenly surpass every other option by a mile. For cases like those, where the payoff is close to the very end, I would not like to see a difficulty increase (I realize we're talking about future items, but I'd like to use examples we're all familiar with).
However, a good example would be e.g. upgrading Varmundt Accessory enchants, which will become quite grindy with increasing levels, but it's not like you're missing out on much when you have e.g. Tenacity lv4 instead of Tenacity Lv5. So it gives opportunity for "bored endgame players" to have something to grind out, without making it excessively harder for everyone else to reach at least some baseline of endgame.
