As for the card itself, Gix is very playable, as both a draw engine and a potent infinite mana sink
The only decks you might not want to run these two are reanimator decks, but otherwise
From my own experience, people often even maligned the play styles that Lord Windgrace offered
After you activate that final ability, your opponent will only have a few turns before they run out of cards and lose the game
Thassa, Deep-Dwelling is the only blink enabling commander that forces you to build a monocolor deck, but despite placing the greatest restriction on your available cards, there are still a lot of powerful interactions it can bring to the table with surprising ease
Soulherder will fit perfectly into lists that run Deputy of Detention, Reflector Mage, and Flickerwisp