There still are some open questions regarding this treatment, that I really couldn't find any guidance on.

Starting with is the business miles divided by lifetime mileage the proper measure of business use or should the business use be measured from the first time the vehicle is "converted" to business use.

For example, lets take a similar example car purchased 8 years ago (and driven 8,000 miles each year) and converted to business use in year 9.  In that year the vehicle is driven 20,000 miles 12,000 for business.  Taxpayer wishes to use actual expenses and claim bonus depreciation.  Are they eligible for bonus depreciation because in year 9 business use was more than 50%?

I think most of us would say yes, but is that situation analogous to converting a vehicle to business use and using the standard mileage rate?