The amount of money in a trading account does not indicate competence as a trader. A new inexperienced trader will simply loose more money with a larger account than a small one. This rule if adopted will not result in the small trader abandoning day trading. If implemented logic dictates that most traders with small accounts will simply trade smaller lots, some will go further into debt through the use of various loans in order to increase their account value to the required limit, and probably very few would stop day trading. A test that demonstrates expertise of the subject is what should determine wether one is competent to day trade or not.
Money proves no such thing.