I think it should have a similar format to this year but with 16 teams something like:

Group A:
England
Australia
Fiji
Ireland

Group B:
New Zealand
Samoa
France
PNG

Group C:
Italy
Scotland
Tonga
Lebanon

Group D:
Wales
USA
Cook Islands
South Africa

Only the top 8 after rankings are published in 2015 should automatically qualify and they should automatically be divided into two pools, Finalists from this world cup should be kept apart in the groups and then have a draw between the remaining 6 teams to fill the remaining places.
2 from each group should qualify.

The system used in 2008 and the system used this year have worked brilliantly in the way they have allowed as many games as possible to be genuine contests.

A sport like Soccer doesn't need super groups because they can find 24 sides that all have at least a small chance to beat each other on a given day, but we will never be there in my lifetime, so our super group concept has delivered us an elegant solution that means 90% of games are genuine contests on the field.

If by some miracle a team like Italy were able to name the best squad in the World Cup, they could still win the cup from the bottom ranked group simply by winning all their pool games and progressing to the knockout stage.

This system can be adapted to fit in up to 24 sides I imagine, and we'd still have competitive games in the group stage by putting the top sides into super groups and having the weaker sides fighting over 2 quarter final spots.

If this world cup makes enough money for us to have dollars to spend on development, we should play as many qualifying tournaments as we can afford, because the experience of the last two World Cups is that qualifying tournaments drive just as much development as the Cup itself, especially in the new countries taking up the game.

true and for me if it was 16, 20 or 24 bring it on I for one love it

As we approach the quarter finals, it is worth reflecting again on how many teams would be optimum in 2017.