Niobium and tantalum are chemically very similar, as should come as no surprise from the names. (In Greek mythology, Niobe was a daughter of Tantalus). The use of niobium as a substitute for tantalum quite possibly isn't patentable, on the grounds that to so use it would be obvious to someone working in the field. If niobium capacitors take off, I wouldn't be surprised to see many companies make them, including Kemet, Vishay, AVX and Kyocera.

In general, I would expect that tantalum and niobium would be found in the same places. What's Vishay doing, reprocessing tantalum ore tailings to extract niobium?