I can say with almost 100% certainty that Maul will not appear in the Kenobi mimi series (at least not S1 if there are more seasons down the line). Here are my reasons why:

1. It would break the lore. I understand if this was a Disneycanon vs. Legends issue, but considering this series and Rebels are part of the same continuity, I Highly doubt Feloni would break with the canon he himself took part in establishing in the first place. Rebels starts at 5 BBY, and Twin Suns happens in the 3rd season, moving it closer to 3 or even 2 BBY, a full 6 to 7 years AFTER the time of this series.

2. It would make for a bad/disjointed narrative. Interviews have all but confirmed a rematch between Vader and Kenobi will happen in the series. Combine that with the Inquisitors, potential flashback sequences, and the storyline involving the as-of-now unnamed female Inquisitor Featured in the trailer; there is simply no room for Maul (unless its in a flashback) without convoluting the narrative.