As with all GPGPU applications, their performance is directly related to not only the speed of the GPU, nor that plus the bandwidth of the connection, but also the processing/data ratio.
If you need to perform a moderate amount of processing on a large amount of data, getting a Titan on a Thunderbolt connection will be completely pointless. It will be bandwidth limited, and you would probably be better just doing everything on the CPU.
If you need to perform a large amount of processing on a small amount of data, or the application is such that the GPU itself is able to CREATE the data as well as process it itself, then the bandwidth restrictions won't affect performance, and a Titan (or six) on Thunderbolt will perform brilliantly.
It comes down to what software, what process, what data, and how much programming skill/effort is involved in the software creation. There is no clear-cut YES/NO to your question.