There is some interest in using nickel iron in electric vehicles as it can produce major long term cost savings compared with some types of lithium. Also, as discussed on the battery comparison page there are only enough known lithium reserves to make roughly 3 million electric car batteries, nowhere near enough. So clearly some other battery technology will be needed, it is just a matter of which.
In contrast to photovoltaic system, obviously power to weight ratio and energy to weight ratio (specific energy) are paramount. Power to weight ratio for bursts during acceleration can always be improved using an ultracapacitor or other storage system in parallel however, but specific energy is a fundamental limitation.
As discussed above, the theoretical limitations of the chemistry for specific energy is 182.5 Wh/kg.
The practical weight is increased by a variety of factors mentioned in the non chemical factors that decrease performance section.
Wikipedia indicates around 50 Wh per kg for flooded cells, but those cells are not designed for low weight so that could be improved upon quite substantially.
Changhong uses nife pocket plate cells for starting batteries (SLI) so obviously they are capable of high rates though it is not clear how high. The starved electrolyte, sealed battery document mentions 6C at substantial efficiency loss. The ultimate electrode for both these ratios is the microfiber metal plaque, essentially nickel fibers around 2 microns wide assembled into a sheet with 95% porosity or so but that may not be needed.
One issue may be the relatively large amount of heat produced during charging, which may be twice or more that of lithium ion, therefore limiting the charge rate, but probably not a major issue.
There are quite a number of papers I have come across whose abstracts describe nife batteries being used to power electric vehicles for city fleets etc. and development projects of various sorts to develop nife batteries suitable for vehicles. It certainly works, it's jut a matter of achieving competitive performance. Zinc bromine may be more suitable for vehicle use, for a variety of reasons.
The discharge efficiency matters relatively more here as overall energy efficiency is less important that for photovoltaic systems probably. The lower it is, all other things being equal, the battery will weight more as the amount of energy stored is lower than what gets to the load, so you'd need a bigger battery.