It is rumored
The rumor came from known leaker Ice Universe, who did not told much else about the Galaxy A (2019) smartphones. Something to keep in mind is that the Galaxy A8 and A8 Plus launched before the Galaxy S9 and S9 Plus. This means that, if the rumor turns out to be true, the Galaxy A (2019) smartphones might be the first Samsung devices with in-display fingerprint readers.
Vivo and Oppo already beat Samsung to the punch with the Vivo Nex and Oppo Find X with new technology, respectively. The Oppo Find X will launch in August, while the Vivo Nex is already available in China and will launch soon in India and Malaysia.
The rumor also suggests that the Galaxy Note 10 will also have an in-display fingerprint reader. That makes sense, since the Galaxy S10 will likely feature the same tech.
Finally, the rumor claimed that the Galaxy S10 will come in three models: 5.8-inch, 6.1-inch, and 6.4-inch displays. The larger two models reportedly features Qualcomm’s in-display fingerprint reader, while the larger 6.4-inch model reportedly features three main cameras.