I thought of a similar plan some years ago: make a balloon out of some very thin light material, such that when inflated, it is very much larger than the satellite. When the satellite is at end of life, inflate the balloon (takes very little gas, as we're in a vacuum.) This greatly increases the drag against the very thin outer atmosphere of the earth. (The balloon will get punctured eventually by other space junk. Without testing, I don't know if it would deflate to smaller cross-section if this occurred. If it would deflate, we'd need countermeasures, perhaps a balloon material which hardens on UV exposure, or spraying some adhesive into the freshly inflated balloon, either way so that it has structural strength to hold shape without gas pressure.)
This is similar to the Japanese plan in that it is a lightweight device you attach to your satellite, which deploys and end of life to speed up deorbiting. In both cases you could put the deorbit device on a dead man's switch, so that it will autodeploy should the satellite fail. I don't know which device would be more effective, except that my device is much more altitude sensitive than the Japanese tether, and that these people are smart enough to think of my balloon but chose to develop the tether.