My conclusion was that Sam slipped up somewhere and lost Ilya. Which maybe because of the reason you mentioned. Previously it seems like it was a 3 cofounders vs 3 non cofounders board split. Ilya switched teams after being upset by something.

If I may wear my conspiracy hat for a second. Adam D'Angelo is a billionaire or close to it so he has a war chest for a battle to hold on to the crown jewel's of AI. Sam has powerful friends but so does D'Angelo(Facebook mafia). I don't think the board anticipated the 90% potential employee turnover, so there is a small chance they leave the board because of that reason. But my guess is there is a 4 letter company that starts with an 'M' and ends with an 'a' that comes into the picture eventually.