How about Toby, Oliver, Duck, Gordon, Henry, Edward, Stepney, and Emily.
Then, while Lionel has the tooling, they can make sets using these prototypes.
I'm not sure Stepney would be popular enough to warrant Lionel to make him, but the others likely would.
I'm kind of partial to the following Thomas engines:
Thomas, Edward, Henry, Gordon, James, Percy, Toby, Emily, Duck, Donald and Douglas, Bill and Ben, Oliver, Harvey, Fergus, Arthur, Murdoch, Molly, Rosie, Whiff, Stanley, Charlie, Bash and Dash, Ferdinand, Scruff, Belle, Stephen, Porter, Gator, Timothy, Diesel, Daisy, BoCo, Mavis, Arry and Bert, Salty, Diesel 10, Den, Dart, Paxton, Norman, Sidney, Neville, Billy, Hank, Flora, Logan, Derek, Dennis, Winston, Stafford, Marion, Stepney, Spencer, Hiro, Connor, Caitlin, and Lady.
I'm a little surprised anyone likes Bash, Dash, Ferdinand, and Charlie. Everyone I talk with despise them, and they're not exactly fans of Neville, Fergus or Dennis. Oh well, each to their own. 
