George: the thing about investing in a computer for music is that it's unlikely you'll use it exclusively for that. I bought a new laptop last fall for running Reason and playing softsynths with but I use it for a hundred other things too. Also you get more technology for your money when you buy a computer rather than a keyboard. That is why software arrangers will eventually come to fruition is because so laptops are coming down in price and many people will own one for other uses anyway.

What may really make an impact on the market would be an arranger controller/software package that are designed to work together. Something like a controller made especially to go with OMB for example. Or a rompler that can be expanded into an arranger when combined with a laptop and dedicated software.