I did a little research in to the rosters of recent U19 teams.
In 2011, seven of the 12 team members played on the 2010 U17 championship team. Those 7 players were Stewart, Tuck, Mosqueda-Lewis, Burdick, Adams, Massengale and E. Williams. The head coach of the U19 team was Jennifer Rizotti who also was head coach of the 2010 U18 team.
In 2013, only 2 players (Turner and Harper) played on the 2012 U17 championship team while 5 played on the 2012 U18 team (Stewart, Tuck, Jefferson, Agee and Graves). Alexis Jones played on the 2011 U19 team. The head coach of the U19 team was Katie Meier who also was head coach of the 2012 U18 team.
In 2015, 2 players (Anigwe and Cox) played on the 2014 U17 championship team; Lou would have been the 3rd but she missed the championships for family reasons. Only 2 players played on the 2014 U18 team. The head coach of the U19 team was Dawn Staley who also was head coach of the 2014 U18 team.
In 2017, no players came from the 2016 U17 team while 5 players were on the 2016 U18 team. The head coach of the U19 team was Suzie McConnell-Serio who also was head coach of the 2016 U18 team.
Precedent suggests two things: First, the head coach of next year's U19 team will be Jeff Walz. Maybe Carla gets to coach the U18 team in 2020. Second, USA BB is willing to promote very talented players from its U17 team to the next year's U19 team as it did in 2011 when 7 of the 12 players came from the U17 team. Given the talent on this year's U17 team, I can see USA BB doing that next year.