I'm actually ok with the achievement/trophy system as it is. I go after them as a metagame, the incentive being not only to play the game, but in ways I might not have without that dangling carrot of an achievement. I 100%'d Dark Souls meaning I played the game pretty much every way imaginable and tapped it for everything it was worth (and then another +100 hours because I love that game immensely); I might not have done so without multitudes of achievements geared towards specific play styles that can't necessarily be enjoyed in NG, or even NG+.
My fear, were they to start tying tangible (so to speak) content behind achievements, is that developers would start gearing their achievements to be award-worthy, read: "if we're giving them something free for earning them, we're gonna make these achievements a B*TCH!" If you recall, in early PS3/360 days, titles frequently just lumped achievements/trophies in as a thing, many games requiring little more than beat the game or complete a couple menial tasks for 1000 GS, but as the generation progressed, they collectively became more nuanced, nodding towards the game within the games. I'm afraid if someone decided to award free shit, the industry would lockstep towards making the awards harder to obtain, like, "beat Dark Souls with the Rock Band controller while the tip of your penis is squeezed in a garlic press, and you get 5% off a yearly XBL/PSN subscription." No, thank you.