Which was done about 8 years ago.... See reply #2.
Yes, the "process-to-DNG" functionality offered by Iridient X-Transformer does what your
Open Directly plug-in does—albeit less flexibly than your approach because the Iridient method only allows the user to launch X-Transformer to process the raw file while your plug-in works with any program.
If the goal is to launch a different product from Lightroom, so that product rather than Lightroom can demosaic the raw data, process it in some fashion, and then return the pixels to Lightroom for either additional processing or just asset management, your plug-in does the trick in a very general manner.
If the goal is to have Lightroom demosaic the raw file and then have another program do something with the pixels, Lightroom's
Edit-In functionality works just fine. It doesn't matter whether you pass the pixels to the other program in a DNG or a TIFF file format because when used in this way they are both just containers for the pixels that were rendered by Lightroom. (My understanding is that when used as containers for rendered images, the DNG and TIFF formats offer essentially the same functionality.)
The point I was trying to make in my earlier post was that
DNG doesn't mean the same thing as "raw." A DNG file can be a container for raw data (the RGB or whatever luminance values recorded by a light sensor) or it can be a container for pixels. But in the latter case, the user needs to decide which program is going to produce those pixels. You only get one shot at that. Afterwards, you can pass the pixels back-and-forth as many times as you like and in whatever file format you prefer, and use multiple programs to modify them.