very misleading storey
FOTA is a team organization which only some of the teams are in. They are not responsible for regulating the sport, the FIA do that.
The agreement FOTA have about kers at present is purely a gentlemans agreement as far as the FIA are concerned. There may well be a contract between the fota teams with regard to kers next season, but it means nothing to teams who aren't in it.
Williams and Force India are not currently part of FOTA and would be free to runs kers next season. Both have the potential to run it. albeit that Force india are unlikely to due to it actually being supplied on a customer deal by mclaren and mercedes.
Williams has a working system but has not currently decided to use it (probably as they cant get the weight distribution to work with it).
There are also the 3 new confirmed teams; Campos, Manor, and USF1. Who knows what these teams will bring to the table but kers is definitely a possibility.
There has been a lot of talk this season about tweaking the regs with regards to making kers have a bigger advantage. Things such as doubling the power it can store, and having a minimum weight for driver and seat. If the regs change then it would make it a must have unlike the moment.
Therefore the situation is a lot less clear cut than you have made out.