The trouble is, this formula is useless for GMs who don’t already have a value for X. Sure, you can set X to any value (including 0), and you won’t break the game. 5e is designed to give DMs total freedom in how they want to distribute wealth, and that’s great. But it doesn’t give any guidelines for DMs who don’t already have an idea how they want to distribute wealth. Lots of folks would appreciate a baseline they can choose to deviate from than to be left to make it up completely.
Yeah, only problem is anything official will then be taken as the holy word.
I mean, you could suggest 1,000 gp per level (so you have about 12,000 gp at 12th level)... or you could go for something more exponential (where you might have almost a hundred thousand at 12th level, and end up in the millions at 20th level).
There really is no impact to it - it's just numbers.
Well, except at the lowest levels, where your wealth dictates when you'll be able to afford a full plate armor.
If you absolutely don't want to make up numbers yourself, my only suggestion is to look at what the official treasure tables of the DMG yield. That stuff has been calculated already.
Only problem with that... is that you'll quickly end up with more gold than you can spend, since there is no magic item economy in this edition. I mean, if you hand out 25,000 gp, you also need to be prepared for the players' question "great, so what can we spend it all on?".
And I lied about it being the only problem

Another issue is that official published hardback campaigns vary hugely. Out of the Abyss, for instance, gives out very little loot overall. Storm King's Thunder is by comparison Monty Haul (and is the only official hardcover module using the DMG treasure tables to any great extent).
The Adventurer's League has its own solution, which is to be incredibly stingy with monetary awards and to keep the heroes perpetually scrounging (relatively speaking at least, I'm not suggesting level 17 heroes have to beg for food). Perhaps you can ask over in the AL subforum for the particulars. (I can't remember any wealth by level guidelines leaking out, but I'm pretty sure they exist internally.)
Then you have another possible solution. If you feature magic shoppes in your campaign, you could do worse just lifting the 3rd edition prices. And if you do, you could do worse than boldly importing the d20 wealth by level figures.
I guess this is what happens when the game designers keep silent on the issue.