According to latest news given by TASS news agency we can expect that even after introducing two new manned spacecrafts, NASA will probably keep using Soyuz spacecraft for delivering astronauts to International Space Station.
It seems that this confirms previous gossips from the late 2016, that both new manned Dragon by SpaceX and CST-100 by Boeing suffer for huge delay. Still NASA being aware of risk of losing any mean of transportation for their ISS crews purchased from Boeing places inside Soyuz spacecraft recently, but deny to confirm that date of introducing both manned vehicles in 2020 is at risk. Now according latest news given by TASS we can take a chance and try to explain what is the backup for NASA in case of Boeing and SpaceX will fail to keep the schedule.
Last year NASA officially announced that CST-100 and Dragon programs have some delay but Agency was not planning to purchase more places inside Soyuz spacecrafts from Roscosmos. Last contract for NASA was covering three flights in 2019 and later every astronaut should take his or her place inside CST-100 or Dragon, it seems that NASA started to doubt if it is possible. According to (21 June 2017) Director General of the Energiya space rocket corporation,Vladimir Solntsev, Company is negotiating contracts for Soyuz flights astronauts inside in 2020 with American company. According to Solntsev, Company is negotiating contracts is Boeing, one of two from main contractors for new American manned spacecraft. It is possible that Boeing being aware of delay with CST-100 decided to purchase some places inside Soyuz in advance to provide NASA a backup in case of introducing CST-100 later than originally planned. Of course it is also possible that Boeing simply purchased this seats to sell them later to any other company or just to use them in future, but if we take under consideration that Government Accountability Office (GAO) report described delay of certification process for CST-100 and Dragon to at least 14 months (May 2017), it is possible that not every NASA flight to ISS (with predicted intensification of flights as ISS is planned to be decommissioned in 2024) will be conducted with Dragon or CST-100. Boeing probably would like to avoid situation, when Energiya could just simply refuse selling places for 2020 or ask for higher price taking advantage from fact that American side would be forced to use Soyuz in case of lack any other mean of transportation.