@Mor - They should worry more about propagating the right kinds of cells instead of developing better pacemakers. They will never be able to make a better alternative than a natural pacemaker (particularly for children), and we can grow most other kinds of cells now, so why not these ones?
I know they are researching this even now, but it seems like a very obvious way to go to me. It's not like they have to grow cells in a complicated shape or anything. It's basically just a patch of tissue that happens to do a particular job.
And it would mean never having to worry about pacemaker implantation or replacement because it would just be a natural part of your body.