Maintenance margin is what the exchange charges the clearing place or whomever to hold your positions into the market close. Day-trading margin is a discount passed unto you, the holder of the contract(s), by the broker, and they assume the rest of the risk associated with your positions you currently have. So if you have a position that requires $10K margin and you have $5K in your bank, but the broker says you need only $500 to hold it, then they are fronting the other $4,500 on your behalf. That is the very very basics of it.
Before this change a US index futures contract at IB had max 40:1 leverage intra day and 20:1 overnight. For a notional 100K contract this would mean $2500 maintenace margin for intraday and $5000 for overnight. Now both overnight and intra day maintenance margin would be set at 20:1, both $5000 dollars IB dont appear to use exchange margin for US SIFs like ES, they seem to use a fixed ratio, currently it is 20:1. For the european DAX index futures the leverage IB offer is currently even lower at around 13:1.
How correct you are, just raised CBOT YM the dow mini by 40%, need close to 10k to hold one contract overnight.