I'm not sure that the normal ND filters will work, as they don't block enough of the IR & UV that the direct sun produces. Especially if the sun is a large portion of the with a super-telephoto.
CMOS sensors for DSLRs already have highly efficient IR filters built-in, and you can always add a UV filter to the ND stack if you are concerned about UV effects. The detail you would get is nowhere near as good as having a dedicated Hydrogen-alpha filter though. I purchased my ND filters for waterfalls and only afterward realized they could be used for solar photography when stacked... so there are definitely better options out there. According to transitofvenus.org, you can use #14 or greater welding glass as an option. I'm not sure if or how that would alter color however. The most interesting photos of the sun I've seen online use an H-alpha filter which brings out a lot of detail.
Here is a photo of the sun I took with stacked ND3 and ND0.9 filters with a 70-200 II, 2x Extender II and a Rebel T2i. I used 1/800s shutter with f/22 aperture at ISO 100 and 400mm focal length. I shot this indoors through unclean windows so that likely distorted the image somewhat. Using a diffraction-limited aperture also reduced sharpness. The dark spots shown are sunspots that I verified using the SDO/HMI Continuum image from the same day. I probably could have focused better but I kept focus time to a minimum to avoid frying things.
Back to the original poster's question, I would say other uses would include 1) really long exposures of waterfalls / the ocean in brightly lit scenes, 2) photos of welding or 3) molten metal in crucibles.