Lets wait and see, but the new EU licensing rules should encourage a crop of new bikes of this size. The 400 isn't marketed in the EU as it's better to buy a 650 and fit the restriction kit - even more so with the new 47 bhp limit and the removal of the 33 bhp limited class.
250s are not particularly popular as learners are limited to 125 cc and they usually want something a bit more than a 250 after passing their test - usually a 500 - 650 which has to be restricted to 33 bhp under the current rules. Again, the new rules will keep them on a 125 for two years after the test, which will make 250s even less popular.
There should therefore be a big market for light sports bikes with just under 47 bhp. This sounds about ideal for a bike of around 300 - 400 cc, so an overbored 250 would probably be a better seller than the 250 in the European market. The Ninja 400 isn't sold here, and it's too big and heavy for the power that it has if it want to be a sports bike. The 500 is now out of production, and was marketed as a commuter. There's a gap in both the market and in Kawasaki's range for a light sportsbike. A 300 - 350 cc version of the 250 would fill that gap, and there's a long history of 250s and 350s sharing the same frame and cycle parts.