Ford is choosing between a revised version of the Fiat 500 platform used for the current Ka or a lightened version of Ford's next-generation B-car platform, part of a modular platform that stretches from the Ford Fiesta through to the Mondeo.
Bringing the Ka entirely in-house will allow Ford more control over the destiny of a model that has enjoyed less success in its second generation. The downside of this choice is that Ford will not then be able to share its development costs with another automaker.