You know, if Govannon didn't come so late in the game he'd be seriously overpowered.
I'm playing a game as the Amurites now, and even though Govannon has only strength 5, he is perhaps the best hero in the game. This "teach spellcasting ability" he has really rocks. I let him get the standard 100xp over time that all heroes get, then I cast Amurite worldspell "Arcane Lacuna" for 20 more xp. Next I completed the "Birthright Regained" and cast "Arcane Lacuna" again for 24 more xp. Now Govannon has taught all my units 9-10 level 1 spells. It's a huge advantage if your champions can cast "loyalty", "courage", "blur" and "haste" , etc. without help from arcane units. Not to mention the great help the easy access to level 2 spells for wizards is if Govannon teaches them before they start using their own promotions...
Best mod ever, IMHO...
