The Bastion system is the right dea. It just needs some polish. Part of the reason for making it an early "bonus" UA is to give it a chance go thru the Playtest vetting process.
Main ways mentioned to improve it are:
Use gp to buy floor space (about 100 gp for 2 squares in about a week). But allow player imagination to furnish it freely.
Use normal core rules like skll and tool proficiencies to work it, as well as background themes and mechanics, and normal economy like hirelings.
Obviously, having a castle-like option is important, but also fanasy options like a Mordenkainens Magnificent Mansion, as well as bastionizing spelljammers, pirateships, and other adventure-accessible homes and business.