This is my guess...
Katie Holmes will convincingly play the role as they continue dating and throughout their engagement, she will soon become Mrs. Tom Cruise and spend a few years, probably less, with him. She will divorce him not long after the marriage ( <18 months ), taking a decent sized chunk of the Scientologist's vast riches. A book deal and possibly a book signing tour (if she is older she'll do the book tour). A subsequent network bidding war for her prime time tell-all will follow along with doing the customary talk show circuit. Everyone will want to know what secrets are hidden within Tom Cruise. She will tell all to Diane Sawyer or Katie Couric. The public will sympathize with her and eat it all up.
This is how she will maintain the publicity that actors/actresses need so badly without throwing her life away on a nut case & Scientology.
The longer they are married the shorter her career will become and the more likely she will to file for divorce. Scientology will be exposed for what it is; Bullshit.
You heard it here.