One thing I love about Madonna, Janet, MJ, George Michael, Bowie and Prince is they all experimented with different genres of music and put a lot of effort into their records. They all seemed like they enjoyed making music and were very hands on in the process. Of course, there was always manufactured pop tarts but had their place and faded away very soon. The 90s in general was such an excellent period of music with artists like Bjork, Fiona Apple, Alanis, Lauryn Hill, D'Angelo, A Tribe Called Quest, Jodeci, Nirvana, Smashing Pumpkins, No Doubt, Imani Coppola, Massive Attack, Jonny Lang, Mariah Carey, Toni Braxton, Alice in Chains, Tupac, Biggie, etc.
But starting in the 90s, a lot of telecommunication companies (television channels, radio stations, magazines/newspapers, websites) got bought out and consolidated under the ownership of five major (now four) companies. This allowed for the push of very clearly manufactured and commercial artists in the late 90s and throughout 2000s and many of the more experimental and talented artists faded away from mainstream or began to cater to more niche audiences. A lot of these manufactured acts like Timberlake, Bieber, Britney, Xtina, Rihanna, J Lo, Beyonce etc all became icons to the young generation but never will have any musical impact or great legacy that will live on for generations after. I think once Madonna dies, her legacy will be legitimized when people actually listen to her music and appreciate her body of work and the amount of diversity and sonic innovation.
While there are still really talented and unique artists out there today. Many of them do things DIY and get followings through social media. They won't become huge or mainstream like Madonna or Michael Jackson because TV, radio and print aren't the dominant forms of communication anymore. We have more options than ever, so people will just go into their echo chambers and listen and watch what they want rather than having to depend on TV/radio for music.
TL;DR: There will be no new Queen of Pop as the concept of pop royalty has become outdated and has become unobtainable too.