The "nominal asset income" is the taxable asset income in that future year in real dollars. So it's the nominal asset balance in that year times the nominal asset rate of return. It is then converted back to real dollars as in all our reports.
The reason it's labeled nominal asset income is so it's not confused with "real" asset income (the asset balance in real dollars times the real rate of return). That value would be different since it would presuppose using the asset balance that had grown by the real rate in the years leading up to the year in question.