I reckon the World Rankings have it about right for the 6n sides going into the RWC, South Africa would probably work their way up to least third if they had a full RC this year. So in order of best positioned for the RWC to worst, in my esteemed and ultimately correct opinion, with more emphasis on Ireland than anyone else:
Wales
Maybe they'd want to add to their attack to beat NZ but after the Kiwis they're setting the standard right now, as long as they don't regress Ireland and England will have to pull out levels of performance that they haven't reached in 12 or 24+ months respectively to have a chance of beating them in a knockout game, SA are a bit of an unknown quantity, nobody else should really beat them. The final is well within their reach given their draw, and NZ are beatable this time around. Very exciting times to be Welsh.
Ireland
Fairly shite six nations for Ireland and almost wholly negative, a lot of players were unfit, and some of the most influential players were out of form dragging everyone else down. Its not all doom and gloom though, we fairly regularly have bad six nations and bounce back:
2011 (3 wins, home loss to France) - depressingly, we had our best RWC ever after that with a great win against Australia.
2016 (2 wins, draw at home) - We had a competitive tour in SA, lost 2-1, with an injury depleted team and players who'd never wear green again involved, beat NZ and Aus in the Autumn too.
2017 (3 wins, none away from home) - Start of the unbeaten streak that would include the grand slam.
That said, and a lot of this has been discussed in the Ireland thread, we need to trust our backs who aren't regular starters. It was clear after Italy that Murray was unfit and void of form, his mechanics were off and he wasn't playing his way back. Meanwhile Sexton wasn't playing great but he was at least having positive influences when not clearly hamstrung by his 9*, another 9 really could have changed our fortunes, Carty was working with far more time than Sexton ever got. Fortunately Murray has 7 months to get himself right, Munster have a good 9 in Mathewson so that means he doesn't have to play if not right and if he gets his mobility and strength back in his arm you'd expect him to come back firing. Sexton will be fine, he'll tear Ulster apart in a fortnight and finish the season strong with Leinster. Problem with this was that even if the half backs were on last year's form they weren't going to be able to show it, the pack looked good in Edinburgh and for 70 minutes against France, clueless for the rest of the competition. Best seesawed between marginally better than what Niall Scannell has shown in his scant opportunities in green and atrocious, if Schmidt values his presence so much bring him to the RWC as third choice hooker but the world cup is going to be all about attrition and Best hasn't proven he can play back to back internationals to a high level since the last 6n.
The few positives were Jordan Larmour, he looked more adept than he had all season with Ster and bolting into the 15 shirt isn't beyond him; Carty is another 10 option behind Sexton and Carbery; Conan finally looked very good at international level; and we have Henshaw, Leavy and Toner to come back who were all fairly vital to success at times last year.
A semi final, final, or even winning the thing hasn't all of a sudden become an unrealistic target though, they'll be going into the competition having won 23 of their previous 26 matches, (Schmidt line from yesterday) Cardiff was the only fixture they played and failed to win in the world cup cycle and the one fixture they didn't play was NZ away and a few of the guys won there with the Lions. That SA or NZ QF is looking far more daunting than it was before though, and it has never been taken for granted.
England
Before the second half yesterday I'd have had them in a comfortably better position than Ireland going into it but I'm not so sure. There's something wrong with their psyche, they were ultra pumped for Ireland and looked like the best team in the world but they looked flat in what was essentially a grand slam decider against Wales when they had worked hard for a lead and their attitude stank in the second half of a home international against their oldest rivals who'd spanked them last year. I think they've got the toughest challenge mentally to overcome (Ireland's challenge is more functional**) and any big successes the squad can draw upon will be more than two years old. There's also Ben Te'o....
I think England are the most well rounded team when it comes to skills but the brains are lacking in more ways than one. They really should be able to beat teams in a number of ways given their big pack and mix of explosive and quick backs but beyond bullying teams into making mistakes and smart kicking they haven't shown much. It's odd.
Scotland
They're not going to win the world cup, they probably won't reach a semi but they'll know that with a fit team they can take Ireland and SA if either fail to properly impose themselves on the game. Yesterday might prove to be huge for them.
France
Brunel isn't smart enough to get France out of that group unless England or, more likely, Argentina gift it to him. Any team capable of playing with a tiny bit of structure with the ability to convert territory and possession into points will beat France comfortably.
Italy
2019 won't reap any positive and groundbreaking final scores for Italy, they'd be best focusing on not ******* up v Namibia and Canada before trying to overturn the two pool b giants.
*I read someone saying yesterday that blaming Sexton's form on Murray was cheap, to blame it totally on Murray is but to suggest Sexton wasn't handicapped at all by slow and erratic service is ludicrous, look at the amount of times yesterday he was forced to rush his kicks despite being deep in the pocket. Coming from a scrum half, the 10 is absolutely entitled to blame you for things when you're providing him with substandard ball and making mistakes elsewhere, it works both ways if the 10 is shirking his responsibilities but that wasn't the case here.
** Some people are going to argue that with things like Sexton swearing and throwing the ball and POM's most memorable line of the 6 nations but I've literally seen both of them do things like that while 20 points up in relatively unimportant Ster and Munster games. The physicality was there yesterday after lacking v England we just never seemed to have any discernible plan the entire tournament, unprecedented from a Schmidt outfit. An eye-test though so anyone is entitled to rebut and disagree with me but to argue it further than that would be pointless.