I suppose a half life with millions of years instead of nanoseconds might be possible. This “unexpectanium”, however, would likely be as extremely dangerous as difficult to produce.
Here’s another thought to ponder. Dark matter may be comprised of these heavier elements. We just don’t know how to look for it, nor how to detect it… yet. If there are islands of stability comprised of these unknown heavier elements, some of which may have a half life of millions of years, it would make sense that they exist in a natural state. They don’t have to wait for mankind to produce them, although we’ll try. Some theorize that this dark matter existed before the Big Bang; all matter that we refer to as lighter elements having been created by some interaction of the dark matter. Hopefully we’ll create a better telescope than the Hubble telescope that can help resolve these issues.
The Higgs boson is now a part of the standard model of particles. There may in fact be others. I tend to think that dark matter is weakly interacting massive particles. They cluster and attract normal matter gravitationally, but pass through normal matter like it’s not even there. The room you’re sitting in could be filled with the stuff but impossible to detect by any conventional means.