There aren't any performance bottlenecks until you write some code ;-)
I think you may need to outline what kind of things you will be `processing` before you can get down to figuring out if there will be any bottlenecks - you'd have to have some idea of the kind of algorithms you're going to use, what kind of data, how much of it how often etc.
Extensibility-wise I recommend scripting. I think xml is highly overrated. It's supposed to be used for giving `meaning` to otherwise meangless out-of-order data and I don't see why so many people use it for meaningless things like config files and the like. It may be an improvement over a proprietary file format that's not human readable, but xml isn't exactly very friendly to read either.
I think you may need to outline what kind of things you will be `processing` before you can get down to figuring out if there will be any bottlenecks - you'd have to have some idea of the kind of algorithms you're going to use, what kind of data, how much of it how often etc.
Extensibility-wise I recommend scripting. I think xml is highly overrated. It's supposed to be used for giving `meaning` to otherwise meangless out-of-order data and I don't see why so many people use it for meaningless things like config files and the like. It may be an improvement over a proprietary file format that's not human readable, but xml isn't exactly very friendly to read either.