1) The original strain (BCS3-L1) is a clinically derived isolate with who knows what properties. Why not just take the well characterized ATCC/DSMZ strain and knock out the lactate dehydrogenase? I am sure the FDA would look more kindly on a better characterized strain - especially since you don't need whatever wild type mutations it has to keep it in the dental microbiome (the lantibiotic does that).
2) Who pays for this? Why? Finding the appropriate payer for a pharmaceutical intervention is difficult. Getting this through FDA trial costs (let's say) $200 million dollars. At the point of sale (PCP, dentist) the competitive product will be...toothpaste and a toothbrush. Getting a patient or insurance to purchase this under current models of care is going to be extremely difficult.