Let's not forget that this is fundamentally an economic question and not just a technological one. "The vast majority of R&D has been conducted by private industry, which performed 70.5 percent ($282.4 billion) of all R&D in 2009." -http://bit.ly/1meroFB (a great study of R&D since WW2). It's true that any of the channels towards strong AI would have abundant applications to sustain them in the marketplace, but BCI is special because it can ride the wave of virtualization technologies that humans are virtually guaranteed to adopt (see what I did there :). I'm talking about fully immersive virtual reality. The applications for military, business, educational training and entertainment of a high efficacy BCI are truly awe inspiring and could create a substantial economic engine.
And then there are the research benefits. You've already put BCI on the spectrum of interfacing technologies which arguably started with the printing press, but BCI could actually be conceived as the upper limit of this spectrum. As high-bandwidth BCI is approached a concurrent task is pre-processing information to improve signal, expert systems are one way of achieving this. The dawn of "Big Data" is spurring more intensive machine learning research and companies like Aysasdi are figuring out techniques like topological data analysis to not only extract meaning from high dimensional data sets, but to render them visually intuitive - this is where the crux of BMI lies.
Imagine full virtual realities in which all of the sensory data being fed into your brain is actually real-world data which has been algorithmically pre-processed to represent some real world problem. For example, novel models could be extracted in real time from a physicists brain as she thinks of them (even before awareness). These models would be immediately simulated all around her, projected through time, and compared to previous models. It is even possible that the abstract symbology of mathematics and language could be made obsolete, though I doubt it.
Betting on such a scenario requires no real paradigm shift, only a continuation of current trends. Thus I am in favor of the "BCI as a transitional technology" hypothesis.