In some ways this switchout is just another tribute that the 2009 V miniseries is paying to the 1983 V miniseries. Or, to paraphrase another sci-fi franchise: All of this has happened to V before, and all of this will (probably) happen to V again.
The Visitors were first brought to the small screen in 1983 by Kenneth Johnson, who at the time was riding high as creator of The Bionic Woman and The Incredible Hulk TV series. During its original two-episode, four-hour run, V garnered a 25 share and over 40 million viewers -- which meant that a sequel was all but assured. In 1984, ABC television rolled out a followup miniseries, V: The Final Battle -- a series produced without Kenneth Johnson.
Johnson cowrote the original Final Battle draft script but ABC decided that it would be too expensive to produce and fired Johnson prior to rewrites. Many of Johnson's ideas survived the transition and thus ABC wanted to credit him as a writer on the sequel series. Likely in protest, Johnson is instead credited under the pseudonym Lillian Weezer. (For the record, you almost never outright refuse a writing credit because refusing endangers your royalty position.)
Thus, firing your showrunner prior to a cliffhanger is a V tradition. So is, apparently, the network wanting to "change the direction" of the series -- a tradition that started before the series even began production. Johnson, you see, originally pitched V without the Visitors as a non-sci-fi miniseries based on a non-sci-fi book. It was ABC's idea to "Star Wars" it up, which may be the only time in history that a TV network has asked for a series to be more sci-fi.
WHAT NON-SCI-FI BOOK WAS THE ORIGINAL INSPIRATION FOR V?
The book was It Can't Happen Here by Nobel Prize-winner Sinclair Lewis -- a political satire written in 1935. The novel chronicles the rise of US President Berzelius "Buzz" Windrip, who won office on the promise of giving every citizen a salary of $5,000 a year (that's about $77,000 in today's money). Windrip quickly morphed from populist hero to outright dictator, and a journalist-led underground resistance formed to unseat him (and his infighting successors) from power.
Lewis's novel became one of the premiere 20th-century fictional cautionary tales of the dangers of unquestioning fealty to charismatic leaders. Lewis was clearly taking a shot at Hitler. Kenneth Johnson arguably aimed his original miniseries pitch, called Storm Warnings, at Ronald Reagan. The current incarnation of V is said to be a criticism of Barack Obama.
Johnson, for what it's worth, wasn't the first to adapt It Can't Happen Here for a more contemporary TV audience. A 1968 TV movie version titled A Shadow On The Land was produced as a longform pilot for an ongoing series, but wasn't successful enough for pickup. That may be why ABC passed on Storm Warnings, but asked Johnson to add a sci-fi spin to the material (and dumb it down, because the original script was "too cerebral" for us poor stupid Americans). In 1983, anything remotely similar to Return of the Jedi was a guaranteed greenlight. Johnson thus made V, with Visitors as explicit allegories for the Nazis -- right down to their jackbooted uniforms and swastika-like emblem (this is what network execs mean when they ask for "subtlety").
Johnson drew on other sources to create the original V script -- notably Bertolt Brecht's play The Life and Times of the Master Race and Damon Knight's classic short story (and Twilight Zone fodder) "To Serve Man." Nonetheless, Storm Warnings was the miniseries original form, and It Can't Happen Here was the basis for Storm Warnings.
Thus, by some measure, Sinclair Lewis wrote the original pitch for V. How's that for Truly Trivial?