choice of toolkits (Score 1)

As has been mentioned, there's a relatively small number of Cocoa and/or Objective-C programmers around. However, you don't need all that many people (maybe only one?), so I don't see this as a major constraint. In fact, I might suggest that you consider going into an even smaller niche. By choosing RubyCocoa (or its upcoming replacement, MacRuby), you might be able to create a framework that would encourage scientists to add their own code. A great deal of Open Source software is written by employees and released by the companies that employ them. This can offer real benefits to the company, in that they may get outside help in the project (eg, in development, documentation, maintenance, and testing). If the code base starts to attract outside attention, the company may be able to have the developer(s) take on some organizational tasks (herding cats :), as well.