They could, but I'd still like the options I listed as part of character advancement. It's not really the amount of gold, its having meaningful options with what to do with it.
I know the current DMG and supplements include some of these options, like downtime activities. However, more can be done there to make those systems more thoughtful (but without having to learn a fiddly new subsystem) and directly tied to the game's economy (I know this part is subjective and highly dependent on the campaign being run).
The Bastion system is moreorless the same thing as real estate. Owning real estate is a player facing option, and belongs in the Players Handbook. The Players Handbook has an Economy chapter. Alongside paying for Hirelings, Vehicles, Equipment, Lifestyle, and so on, there also needs to be options for real estate.
Real estate is notable because it comes with important narratives and in-world immersion. Estates like a home or hideout, business operations, living on a pirate ship or in an other plane, along with magical amenities, offer inspiring flavor. The estate, or "Bastion", is especially where players spend their Downtime. The estate helps center a campaign in a way that avoids a feeling of random murder-hobos. Players can build a nest and from there work toward a narrative goal.
The challenges of a Bastion system are:
• Focus on how to choose and build estates, and what their various benefits are.
• Integrate estate building with normal rules like construction costs, Downtime, Lifestyle, and Hirelings including spellcasters.
• As part of the Players Handbook, the estates are the ideal place to spend gp.
• Yet, the estate must motivate players to adventure, rather than "trap" them at home away from adventuring.
The last concern is the trick of a Bastion system. Players need to want to adventure for the purpose of building up their Bastion, which is a means to accomplish their longterm ambition while advancing across tiers. One character might want to be a sovereign over a territory, an other to become an immortal wizard who runs a school, and the Bastion can be part of these ambitions.
