Yes there is going to be a new series called Avengers Assemble. I seen some of the art for it. Hawkeye no longer wears a mask like his movie counterpart. No it's not a new continuity. What he said. Now getting back on topic. No, a film is never announced without a script. You can't even pitch an idea for a movie without a script. That simply does not happen. Now as for filming a movie before a script is done that does happen however not the way you're thinking. You do realize a script goes threw multiple drafts. They don't just write up one draft and film that without making any changes to it. No script means they don't even have a first draft yet. They're not going to make it up as they go along, they have to have at least some rough idea of what they're going to film before any other work can even get started. Technically speaking every movie ever made was made from an unfinished script. A script is meant to be performed not read so a script by definition is an unfinished work.