Actually, the Clearing Fund Formula accounts for Margin Requirement Differential, so margin is indeed a component of the amount posted.
More importantly, cash requirement effectively reduces the amount of leverage that customers are able to use, and that means (A) no additional firm capital needs to be lent for purchases of GME or whatever other stock, and (B) margin-account customers trade less on a given amount of their own capital.
Are you suggesting that Robinhood would be required by Procedure XV to post more than $1 for every $1 of GME stock that a customer buys in a cash account?
I'm not sure I follow why the future actions of Robinhood customers matter. They've executed the number of trades they've executed, DTCC raises the collateral requirement for meme stocks, and now they're on the hook, whether stocks were purchased on margin (implicitly or otherwise) or not. You've got the rules in front of you. They seem to plainly say that Robinhood has to put up collateral regardless of whether margin is involved.
Again, I think the margin stuff is mostly a red herring?
More importantly, cash requirement effectively reduces the amount of leverage that customers are able to use, and that means (A) no additional firm capital needs to be lent for purchases of GME or whatever other stock, and (B) margin-account customers trade less on a given amount of their own capital.
Are you suggesting that Robinhood would be required by Procedure XV to post more than $1 for every $1 of GME stock that a customer buys in a cash account?