A lot of people have been worried about potential game breaking bugs in the initial Steam release - which could have a devestating effect on the new players on Steam. I know Zacks's bug testing has been quite thorough for this release, but given the breadth of play styles and interactions in DF it seems quite possible he could have missed something.
After all, the initial releases of all previous updates contained a few major crashes and game breaking bugs. Now, all of these have usually been fixed quite soon after launch - a testament to Tarn's skill - but with this release, the initial impression will be way more important than usual.
As such, I propose doing a semi-closed beta for a few weeks before Release, by giving out Steam keys to one hundred Patreons chosen at random in a raffle. That would have multiple positive effects. It would reward the Patreons. It might inspire people to sign up to the Patreon, to take part in the raffle.
And it means the people chosen likely have diverse enough knowledge of the game, and different enough styles of play, to thoroughly test every facet of Dwarf Fortress.
Finally, it would give Tarn enough time to fix these bugs, should they crop up during the playtest.
Additionally, it might be a good idea to invite important community members to the beta. To update the wiki, create video guides, update the mods, port over DFHack and potentially start work on tilesets - to give the Steam players access to everything this community has to offer.
It just seems like an elegant way to make sure that by the time the public is given access to the game, it will be in prime condition, ready to be enjoyed without too many hurdles. And it's a nice little way to involve a few of the games Patreon supporters in the development process - as a little reward for their support.