There are two conflicting studies on the use of baking soda for lactic acid buffering that I am aware of. One said it was of no use, the other found some increase in performance for events greater than 1 minute and less than 7 minutes.
Either way, the user will suffer massive and violent diarrhea within 15-30 minutes that may leave them somewhat dehydrated. As well there are long term risks to repeated use because of a condition known as 'rebound hyperacidity' which tricks the stomach into producing large amounts of acid in order to find proper pH due to the base solution. Long term users suffer from bloody stools and intestinal damage.
Taking a substance that jeopardizes a rider's health or creates an unfair advantage should be considered doping whether it is allowed by the UCI or not.