Airbus A318 has 2 engine options, CFM56 & PW6000 dedicated for A318.

But I think the decision made by Pratt Whitney of making PW6000 just for A318 & not for other aircrafts like B717 is not wise at all.

First of all, there would be very few PW6000 produced since A318 is the only aircraft to use PW6000 engine. This in turn rises production costs & prices.

Secondly, this greatly increases cost of maintenance because PW6000 uses the parts very different to V2500, which is a JV company between Pratt Whitney, Rolls Royce, MTU of Germany & Japanese Aero Engines Corporation (JAEC). This in turns makes the engine even less attractive.

So it is much better to design a lower power version of V2500 to power A318, like that of CFM56, rather than making a totally new engine for it.