This has been fairly widely reported already, but Southwest updated their Companion Pass terms and conditions on 1/1/17 to include the following:
Points converted from hotel and car loyalty programs, and e-Rewards, e-Miles, Valued Opinions and Diners Club will no longer count toward qualification for a Companion Pass.
Most importantly, they are eliminating the ability to use Marriott Hotel + Air packages to earn the Companion Pass, which could have been done with 270,000 Marriott Rewards points or 90,000 SPG Starpoints. The other options they are eliminating are more useful just for topping off your account. This is a big loss if you were planning to redeem Marriott or SPG points for this in 2017.