I mean NO ONE was working on gas phase Ni-H in those days. Or nanoparticle Ni. As far as I know, no one was. Perhaps Rossi was, while keeping a low profile.
Many variations that seemed promising back then, and some still do. They include nanoparticles, nanoparticles in various suspensions such as aerogel, glow discharge, the mysterious 1930s reactions with carbon the Mizuno has been replicating, Liaw's molten salts, bulk materials with various stimulation techniques, and various combinations and permutations. At any time in the history of cold fusion, there have enough promising approaches to keep a hundred major laboratories fully occupied. We have never been short of promising experiments, but always woefully short of people, equipment and funding. For all anyone knows, some of the other unexplored techniques may be much better than Rossi's. Mizuno may have discovered or rediscovered three methods superior to Rossi's. - Jed