According to my latest TeslaFi totals (11-May-2018), 88.2% of the active cars (1711) are using 5 different firmware versions right now.
2018.18 276 16.1%
2018.16 209 12.2%
2018.14.2 548 32%
2018.12 313 18.3%
2018.10.4 165 9.6%
Totals 1531 88.2%
2018.18 276 16.1%
2018.16 209 12.2%
2018.14.2 548 32%
2018.12 313 18.3%
2018.10.4 165 9.6%
Totals 1531 88.2%