This is the march of the nines. 99.8% is nowhere near ready for mainstream release. This metric would result in a crash one in every 998 drives. Current human averages are an accident for approximately every 200,000 miles. Tesla would be looking to improve this 10X for an accident rate of one every 2 million miles. At this rate, for FSD Level 5, Tesla needs a 99.99995% success rate. It will never be perfect, however the FSD crash rate needs to be significantly lower than current human averages to gain full acceptance by governing juristictions.
EDIT: Ha ha. What @adiggs said.
Yeah yeah I know, my numbers weren't precise. I was merely stating that Elon wants a high degree of safety certainty before releasing Level 5. 99.8% was incorrect, I think Elon's actual percentage was 99.9998% or something?