They could just make it crazy expensive or have guilds pay exorbitant rents. That would still limit housing to a few guilds without this whole RNG business.
It's sad, but that's exactly what i'm expecting, like they could easily implement just the Guild housing without a dungeon, when i read/heard they wanted to put a dungeon on it, i just rememberd RO1 WoE guild dungeons instantly and their very expensive tax to get access into it. And yeah, this is a problem that have/had RO1 and RO2, about limiting housing to few guilds that can afford zeny and have actually "power".
They could just make it like Aura Kingdom without any guild dungeon and for every guild, but no, they had to put a dungeon on it with RNG, zeny tax and for a few top guilds.
You're right, they want to sink zeny, like on RO1's Rachel Sanctuary quest "donate 500 million zeny" (server wide) to get access to the dungeon......