I read online that Sprint (who owns Boost) is only going to allow the S10e to be on the boost network initially. My guess is that once the phone has been out for 6 to 12 months then they will sell the s10 on Boost. To have the new phone from the beginning you will need to go to a major carrier as they don't want to lose business to their subsidiary.
Here is a direct quote that the Boost Mobile customer service wont take the time to find, posted on Feb 20th:
"Galaxy S10e Coming to Boost Mobile
Samsung Galaxy S10e can also be paired with no-contract plans from Boost Mobile giving consumers an additional way to save and find the best option to fit their needs. Galaxy S10e in prism white will be available for purchase beginning on March 8 in Boost Mobile stores and at www.boostmobile.com."
Which again tells nothing.
It only states that a Boost branded S10e will be available for purchase.
Last year same thing with the S9+ fully paid for Sprint branded and unlocked worked on Boost.