Apparently there was barely any change from the playtest version.

Key points:

• Bastions are acquired at lv5.
• Each player has their own bastion. Bastions can be grouped together into one bastion, but they are still treated as different bastions for the purpose of mechanics, except that grouped bastions can defend each other from attacks.
• Bastions can be populated with "basic facilities" (whose only purpose is flavour, apparently) and "special facilities". The latter provide actual tangible benefits by issuing orders to them during the "bastion turn" (once every 7 days). Special facilities are acquired as the players level up: two at 5th and 9th level, and one more at 13th and 17th level.
• Both types of facilities come in three sizes: "cramped" (4 squares), "roomy" (16 squares) and "vast" (36 squares), and can be upgraded later on. Some special facilities may have a minimum size requirement.
• The article provides three examples of special facilities. I'm not going to copy-paste them (click the link, you cowards).
• Project Sigil (WotC's own Virtual Tabletop) ad. Multiple ads, actually. My God stop talking about Sigil pls.
• Attacks seem... Lackluster. "In the event of an attack on your Bastion, a number of d6s are rolled. For each die that rolls a 1, your Bastion loses that many Bastion Defenders. If you don’t have any Bastion Defenders or lose them all in an attack, a random special facility is shut down for your next Bastion turn." Bastions that are grouped together can sum up their defenders total.

From what I'm reading, there are very few changes from how it worked in the playtest. I guess they were either lazy, didn't have enough time to integrate feedback, or both. This thing only exists to sell Sigil.