Basically it’s allowed but they must properly mark it as NSFW, so it can be filtered out for minors and people who are actively trying to avoid it. More or less they’re making the sharing of adult material a more legitimate thing for twitter, which is kinda hard to tell because twitter has always been filled with porn but I guess it’s just more official.

Wherever or not people will actually mark their content as NSFW or if Twitter will enforce it is in the air. I’ve seen Twitter content sensitivity setting used more for video game spoilers than it’s actual intended use.