I needed this WordPress plugin, named ILC Rich Title for a particular work I was in. I had to enable rich text editing for the title field on the edit post/page area. In fact, the customer only wanted to add some line breaks, but I added the whole TinyMCE to it. I’m not sure if this exists for the title but I researched a lot and didn’t found one.
What I did found was the TinyMCE Excerpt plugin by Simon Wheatley which enables TinyMCE for the excerpt edit field. Changing the jQuery wrap that TinyMCE Excerpt performs by targeting the appropriate title div, #title (with the help of the ever loved Firebug) I got what I wanted. After that it was a matter of triggering wpautop for both edit area and rendered content, using the edit_post_title for the former and the_title for the latter. Now, since I’m using the_title, it means that it will enclose into p all the titles so be careful when setting your css for titles.
ILC Rich Title is hosted on WordPress plugins repository. You can download it from there.