the only reason bitcoin is a store of value is because people anticipate it will be useable for daily purchases.
Using a globally distributed and persistent blockchain entry to by a pack of Skittles is about the most brain-dead use of resources that I've ever heard of. This is the proverbial use of a sledgehammer to kill a fly.
I agree with that to a point...however, it is worth using it to make a micropayment of say 2 cents to instantly read some content on the internet (something not currently possible with existing payment systems because of unreasonable high minimum fees).
Which means tracking capital gains or losses "could" be a stumbling point for this "best use" of the technology. But I still believe that a bit of code can solve this problem to provide the necessary tracking and documentation.