Yeah I'd say your guess will be right. 90's and Y2K names will come back in a big way, they are already starting to creep in. By 2100, 90s-00's babies would be the great-grandparents (or great-great grandparents) and that seems to be a popular naming cycle.
I think religious names will actually get MORE popular, because religious people seem more interested in having kids. There may be more atheists/ agnostics than ever before, but they aren't the ones with big families. I think we'll see a (even more than now) stark juxtaposition, of trendy/unique names next to super conservative religious names. And I think "foreign" names will be a huge contributing factor as climate refugees and migrants from booming populations overseas become more prevalent. Indian names in particular will start to become more mainstream.
Looking at the bottom of the US lists, I wouldn't be surprised at all if these names were somewhere in the Top 100 by 2100:
Abner,
Ephraim,
Eliezer,
BoazMary and
MariaYousef,
YaakovDarwinVir or
Veer (m)
VanZevAyah,
AyaNames ending in -ani for girls - Aylani, Kahlani, Laylani, Meilani,
AvaniNames of 90's "It girls" -
Whitney,
Lisa,
Shannon,
Winona,
Andie,
Cindy,
Julia,
Jennifer,
Yasmine,
Monica,
Aaliyah,
Brandy,
Britney,
Christina,
Denise,
Liv,
Uma,
Nia,
Renee,
Gillian,
Gwen, Jodie/Jodi,
Mariah,
Aishwarya, Raveena, Sonali