Univision has already secured viewership parity with the US' 5 main English language networks (often coming in 5th on overall rankings). The growth of the Hispanic and Latino demographic in recent years has fueled this trend and there is no reason that this can't continue. It is only logical that following this growth curve, assuming the networks target demographic continues to grow, Univision should be able to not only equal the size and scope of the other major networks; but surpass them.
Univision will have continued success and growth. As the Hispanic population grown in the United States, the number of people watching Univision will grow with it. I think Univision will grow to be considered part of the "big" networks alongside ABC, CBS and NBC. It already has shows filmed in the US and watched in the US that beat ratings for several network shows.
No, Univision will not ever be as big as the major networks in the United States, because it is meant to serve a specific part of the population. Just as Fox News has a certain demographic, so does Univision. Univision is great, but it is not so universally available as the major networks. It would take a long time for Univision to become as popular.
While at Univision states that Hispanics are fueling the growth in America the Hispanic population only accounts for 17% of the total population of the U.S. The number of Hispanics in America may be growing year on year, but they are very unlikely to outnumber the English speaking population. The major networks in the United States have the majority of viewers, and I do not believe that Univision will be a major competitor.