Daytime can be limiting. Just ask 1995 Emmy nominee Sydney Penny, who plays rape victim Julia on ABC's All My Children. ''We still can't say scumbag,'' she says. ''We're not exactly addressing the real world.'' And her current story line, a will-they-or-won't-they-do-it interracial romance, has been tame. But as cohost of the ABC clip show Hot Summer Soaps, Penny, with four other ABC daytimers, will deliver dialogue decidedly more real, since much of it will be improvised. Penny played young Meggie in The Thorn Birds but came to daytime prominence as a sex-abuse survivor on Santa Barbara. She joined AMC two years ago, ''tired of playing the victim,'' but then her character was assaulted. ''They're handing me this great story and I'm thinking, Hey, can't I just jump out of a birthday cake?''