I think that it would make Rugby Union (and probably Rugby League) more interesting if the person who scores the try has to kick the conversion.
It is their try, so why shouldn't they.
It would make things interesting when a team pushes over for a scrum. Would you let you better kicker score? Or just put it down and go for it? Would you risk passing it in the goal area to a better kicker?
It might see more tries to the better kickers, but it would stop such an emphasis on the main kickers.
Penalties should remain as free choice.
What do you think?