There will be many new rules on the WTA Tour, starting in 2018.
To begin with, as explained by TennisLife, all WTA tournaments, including the Slams but excepting the Premier Mandatories, can award 'top-20' wild cards to non-top-20 ranked players. Until the 2017 season, only the WTA Internationals could award such wild cards to players ranked outside the top-20.
Like in the ATP Tour, a strict time-limit will be enforced within points in the WTA Tour. If a player, who is serving, fails to serve within 20 seconds (after having been given a previous warning), she will lose her first serve. The returner, meanwhile, will get a point penalty for the 20-second time violation.
Another interesting rule change is about players returning from maternity leave. Unlike those players, who were making a comeback to the Tour after injuries or illnesses, players returning from maternity breaks had to play their first tournament within a year of their child being born. Now, starting from 2018, there will be no time limit (as in the case of injury and illnesses'-related comebacks) for players returning to the Tour after having a child.