Allow unfiltered HTML in titles for low level users?

Set it up so that your editors and writers use the default title as the first line and add a metabox for a subtitle that will output the other lines as separate lines. This will require a theme adjustment if you want them all included in the h1 header tag. With some adjustments to the admin theme you can get this metabox placed under the title entry field, which should help reduce confusion.

The way WordPress prevents HTML from titles isn’t able to be overridden. It’s possible only if you hack the core but, even then, it creates a lot of strange problems. Feeds can’t handle HTML in titles and the permalinks behave wierdly unless you rewrite the permalink functions. Leaving the default title alone and using custom fields is the way to go.