http://www.ianjameskay.me.uk/KickOff2_WC2018.xlsx has results for World Cups 2018, 2017, and 2015.
I can have a go using the last four (or five) world cups only, if someone can point me at the results from 2016 (and 2014)?
However, I'm going on holiday before the Bremen World Cup, so I may not have time before then. But here are some suggestions.
100 points for a win, 50 for a draw, and 1 for each goal difference.
So if you win 1 game by 1 goal, and lose all your other games by a combined 100 goals, your score is 1.
2xpoints for Silver Group. 4xpoints for Gold Group.
Knockout games use aggregate score, excluding extra time/penalties.
2xpoints for Bronze knockouts, 4xpoints for Silver knockouts, 8xpoints for Gold knockouts.
Knockout points are doubled if the winners can still win a trophy: 1st v 2nd, 17th v 18th, 33rd v 34th, Gold/Silver/Bronze semi-finals, all quarter-finals.
2018 WC carries 100% weight, 2017 carries 70% weight, 2016 carries 70%x70%=49% weight, 2015 carries 70%x49%=34.3% weight etc.
All the calculations will be public in a spreadsheet, although it may not be pretty.
What do you think? Don't just criticise, suggest alternatives.
I probably won't take into account strength of opposition, that is complicated. And so is considering national tournament results. If Alkis can send me what he did, and describe it, I'll have a look, but it may be too much work.
Tournament organisers do not have to use World Rankings for seedings. In Wimbledon tennis, they adjust seedings, usually for great players who haven't played a lot of tournaments (Serena Williams, Dagh).