Assuming that the basic Slugga boy will be 6 points (and I don't see any reason to doubt that rumor now that all the rumored weapons stats turned out to be true) I really think they came up with an elegant way to balance trukk mounted armies vs. foot sloggers.
The big problem before was that the achillies heel of the Ork boy was his slow speed and his vulnerability to enemy fire. The KoS negated both these issues in 3rd edition which made the KoS a powerhouse army while footsloggers had to struggle to win anything.
4th edition partially nuetered the KoS with the introduction of Entanglement. Of course this really just made KoS games into an all-or-nothing proposition: If the KoS player had ample terrain and got the first turn he would be able to charge at will and destroy the enemy. If he didn't have these things his Trukks would get torched and all his units would waste a turn being entangled before getting shot to pieces.
By reducing the effectiveness of the basic Ork boy in this new codex but also reducing their points cost by a third (from 9 points to 6) means that basic footslogging mobs get to utilize the new strength of the Orks: numbers (plus they get the 'once a game' fleet move too).
Point for point the new Slugga boy (without a Choppa but with Furious Charge) is superior to the old Slugga boy. For example:
- 10 Old Ork Slugga Boys (9 pts) = 90 pts.
- 15 New Slugga Boys (6 pts) = 90 pts.
- vs. 6 Space Marines (15 pts) = 90 pts.
6 Marines will cause an average of 1.25 failed saves against Orks in a round of combat.
The old Ork boy would get to swing simultaneously with the Marine at I4 so all 10 boys would get their full attacks on the charge. Even so, all 10 Orks would average 3.3 failed saves against the marines.
The new Orks don't strike simultaneously even when they charge, so on average they're going to lose either one or two models before they get to swing. Even with losing two models ahead of time, the new Orks still cause an average of 4.29 failed saves against the marines and 4.62 failed saves if the Orks only turn out to lose a single model before they swing.
With both new and old Orks fighting in a round of combat where they didn't charge the marines would strike first so they will lose some models before striking. However since new and old Orks still die at the same rate (they have the same defensive statistics) the fact that you'll have so many more new Orks makes losing models before getting to swing less painful.
In a round of combat where neither the 6 marines or the 10 Old Slugga boyz charged, the Orks would cause an average of 2.23 failed saves against the marines assuming the Orks lost only a single model before it got to swing or 1.98 failed saves against the marines if the Orks lost two models.
The same scenarios with the new Orks (15 new sluggas vs. 6 marines), the Orks will cause an average of 2.29 failed saves against the marines if the Orks lose a single model before it swings or 2.13 failed saves against the marines if the Orks lose two models before they swing.
In other words, no matter how you look at it, the new Ork is better off in combat than the old Ork unless we're talking about fighting against 2+ save models. The flip side of this fact is that the new Orks are vastly better against non-MEQ armies like Tau and IG where the lack of a Choppa and I4 doesn't really affect anything (whereas the ability to field more Orks does have a huge impact against these armies).
But getting back to the KoS, the fact that the mob sizes are still limited by fitting into a Trukk means that the Trukkboy mob isn't able to tap into the core advantage of the new Ork statline: strength in numbers. Also small unit sizes means that each individual Trukkboy mob is much more affected by leadership issues than a big footslogging mob (which is fearless when numbering more than 10 models). Heck, we still don't even know if Trukkboy Nobs will be able to take the 'big horn' +1 Ld upgrade!
Of course, the reduced boyz points cost will mean you should be able to afford more Trukkboy units in your army and the rumored Trukk bailin' out rules means that games with Trukk heavy armies will be much, much less all-or-nothing.
All that means your individual Trukk boy mobs and boyz will be less effective but you should be able to reliably get more of them into combat in your average game.
To me that means that the KoS type army sounds more balanced and fun to play with and against and the footslogging Ork horde will be (as needed) much more effective than it previously was.
So is everything all sunshine and roses? I'd say no simply because tournament organziers continue to puch the upward limit of points values in their games without properly adjusting the time allotted to play the games. Ork horde players already struggle to finish their GT games and now they'll have even more Ork models to deploy and move. Even more dice to roll each shooting and assault phase. And the 'ard boyz tournaments have set a new ridiculous standard of 2,500 point games in 2 1/2 hours.
Of course, this isn't the fault of the games designer. I think the reduction in points cost of the basic boy is the perfect solution to many of the issues of the Ork codex. It is now up to tournament organizers to get it through their head that they need to lower the points values in their tournaments or allow more time for each game.