am I understanding this correctly?

the cards from Goblins vs Gnomes and Naxxramas will NEVER return to standard?

also the cards from League of Explorers, Grand Tournament, and Blackrock Mountain will never return to standard either?

also Hall of Fame cards can get dusted again? don't care about Wild/Brawl

Blizzard reserves the right to do anything they want. Hence, some inconsistencies (base set isn't supposed to rotate out but they rotated some of it out, Blizz said they don't like OTK combos & nerfed most of them out of the game but then this expansion brought new OTK combos into the game, etc).

The short answer: Once cards rotate out, they're out of standard for good.

man that is so weak. I waited so long with all my golden GvG cards, could've dusted those a year ago

Yes once a set rotates out it's Wild only forever (barring some new format or if Blizzard decides to do something different).

The only set that will always be Standard is Classic. Every new set will eventually rotate out.