Might Eliza Dushku be cast in the pilot for “How I Met Your Dad,’’ the spinoff of the CBS hit “How I Met Your Mother’’? Maybe. The Watertown-bred actress implied as much in a tweet the other day to her 1.5 million followers on Twitter. The former “Dollhouse’’ star said she’s reading the script, which stirred up her fans. “#Reading the pilot, folks. No announcement, just a first date,’’ she tweeted, adding that the script by “HIMYM’’ creators Carter Bays and Craig Thomas and “Up All Night’’ creator Emily Spivey “IS kinda #badass.’’ Greta Gerwig has already been cast in “How I Met Your Dad’’ as the central character, a woman who’s realizing her recent marriage was maybe a bad idea.