Yeah, there is a good chance that it will be Epic Store Exclusive for 1 year on PC sadly. Why do I think that? Borderlands is published by 2K, a subsidiary of Take-Two, and Take-Two's Private Division publishing label recently took Epic's tainted money to make Obsidian's The Outer Worlds Epic Store/Windows Store exclusive. Since we know that Take-Two is willing to take Epic's money for exclusivity, it is very possible that Epic has paid for Borderlands 3 as well.
Even without all that, you can tell because the lead dev tweeted many messages in regards of support for EGS lol.
Ah well, I still need to play and beat Borderlands 2 and the Pre-Sequel.