It happen around April 5th of this year. Here is an
article on it.
It means you can only get 1 Southwest Card at a time. So if you plan on getting both personal cards, u wont be able to. (ie get one card in March 2018 and the 2nd personal card in August)
You can however apply for both cards at once to get both cards but you would need to spend $4,000 within 3 months.
You can however go 1 personal card and 1 business card.
You can also wait for the
rumored "Premium" SW card that has a higher bonus.
hope that helps.