The likelihood is great! In fact ONE IS FORMING as we speak. It is called LOIHI and it stands about 3 km off the sea floor. That is, the ocean is about 5 km deep and Loihi is a SEA MOUNT that starts at 5km deep and gets to within about 2 km of the surface. At the summit of LOIHI is a BIG caldera. It is estimated that in about 100 000 years there will be a NEW Hawaiian island...there will be new real estate. Loihi is South west of the big island Hawaii.

Good question! I'd say the likelihood is 100%, since a new volcano is forming below the sea RIGHT NOW and has grown so much that it is pretty close to breaking through the surface of the sea. The new volcano is named "Loihi", pronounced low-ee-hee, and it's about 30 kilometers south of the Kilauea volcano on the "Big Island" of Hawaii.

The Hawaiian Islands are actually much, much larger than they seem, since they begin at the sea floor, which is almost 15,700 feet deep where the Hawaiian Islands are located. The tallest Hawaiian volcano, Mauna Kea, is actually taller than Mount Everest if you consider that it rises from the sea floor (15,700 feet) and sticks up out of the ocean an additional 13,800 feet, giving it a total height of 29,500 feet. Mount Everest is about 29,000 feet tall. This information is from the US Geological Survey. Other sources claim Manua Kea is over 33,000 feet total.

Loihi also started at the sea floor, and is now about 3,000 feet from the surface of the ocean. From our perspective, it will be a long time before it actually breaks the surface to form a new island, but it's already made it ~80% of the way there!

The University of Hawaii and the US Geological Survey both have web pages devoted to the new volcano. You can find them at:
Hawaii.
Volcanoes.

There is, in fact, a new island forming just south of the Big Island of Hawaii. It is called Loihi and scientists are collecting information about the rock types and the biology down there. For more information about how they get data and what its bathymetry (ocean floor topography) looks like, visit Hawaii.