I've been thinking a little more about the combat math. reading between the lines of the seminar, we can assume that Attack bonus (or its 5E equivalent) will scale slower than in 4E.
One aspect of this may be the removal of magic item bonuses as default.
The current math is 10 + 1/2 level + Ability Mod + Magic Item bonus + potenial feat bonuses. Overall I think you end up with a figure thats roughly +1/level (for min-maxing one ability score); although with starting ability scores you are probably looking at more like +4/+5 boost to start and then +5/6 levels.
If we remove the magic item bonus then that drops to about +4/6 levels.
However, 4E works on a rough framework wherein enemies are only really relevant +/-5 levels, with a +2.5 level swing (in the PCs favour) per tier - although that last bit is aggregate damage based rather than to hit based.
Lets assume WotC wanted to double the threat range relevance of monsters from +/-5 to +/-10. I think they would firstly need to reduce the attack bonus scaling to +1/3 levels.
4E attack bonus at Level 1 = +0, At Level 20 = +10 (+7/3 AS, +4 MI, +1 FE) = +22/+18
5E attack bonus at Level 1 = +0, At Level 20 = +6 (+7/3 AS, +0 MI, +1 FE) = +14/+10
Dropping to a +1/3 attack bonus model and removing Magic Item bonuses as default we can drop the progressive increase to 55%. Thats good enough to take us from a +/-5 Level spread up to a +/-9 Level spread. Meaning a Level 1 Goblin will still be (just about) relevant in terms of math against 10th-level PCs.
Taking this as default means we also have to apply the same factors to damage. Meaning that instead of damage doubling every 15 levels (for PCs and monsters) it would instead double every 25 levels (at +15.75% every 5 levels). Of course another option might be to keep damage progression roughly the same as 4E (since many 4E campaigns seem to think monsters have too many hit points in 4E and deal too little damage).
Anyway, just more waffling on my part.
Edit. Just read the new seminar and it seems that Ability Scores won't scale as quickly and (potentially) have a mortal cap (possibly 20 + racial modifier?).
So it Attack Bonus is +1/3 and ability scores only go up to 20 ish (I'm guessing) then we could definately have that +/-10 level spread for the math.