In my playthrough he just made comments about various locations, ie in forests he was worried about being attacked by elves, the undercity reminded him of home, etc.
As far as I know there are no quests involving Baeloth. Unless you count the Black Pits.
Precisely my experiences as well. He's a great NPC even so, but it would have been even better with a quest. It would have been particularly interesting to have the rest of the party temporary "disabled" and having to rely only on his spells for a short while. Considering his spells are more or less decided for you, you could probably come up with some very fitting challenges.
Perhaps a quest for Mr. B. could be made available in a future DLC. Time will tell. The devs must be brimming with ideas about all sorts of neat things that could be developed.
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As far as I know there are no quests involving Baeloth. Unless you count the Black Pits.