UPDATE: It occurs to me I made a huge mistake here. In addition to DEALING less damage, since it takes less damage to fell an enemy, the damage they do over the course of an entire encounter is substantially less. Therefore, damage to be "equal threats" scales at a much slower rate than I noted here.
There've been hints (not exactly in great detail) of toying with the idea of what I call atomic scaling of damage. The idea, as I understand it, is that an orc is an orc is an orc; rather than having a 5th level monster whose "longevity" as a threat is done away with due to attack and defenses scaling, a monster's "level" is a function of its HP and its damage. Therefore, an orc at 5th level (I don't have hard stats so we're just talking in the abstract) is as dangerous as 5 orcs at 10th level (or 15th level, or whatever), not because it's suddenly a minion and thus has higher attack and defenses but less damage and the like, but because an orcs damage at 10th (or 15th) level is 1/5 that of 5th level.
Here's my problem: the math quickly proves untenable. Let's assume that orcs are actually a 1st level threat-you think "Oh there's a party of five orcs. My party of 5 PCs will be reasonable challenged by them." Now, let's assume that there is a monster that deals so little damage that even a single PC can take out five of them. Let's say that this applies to kobolds. Thus, our atomic damage rating is measured in "Kobolds." Finally, let's assume that there are such monsters that we expect them to be able to challenge an entire party at 1st level all by themselves. Let's call them "Adult Dragons." We can define kobolds, orcs, and dragons, using kobolds as the common unit.
1 Kobold = 1 Kobold
1 Orc = 5 Kobolds
1 Adult Dragon = 25 Kobolds
So, we're not past 1st level, and already, in order to keep to the "danger is purely a function of damage/HP" we have to have one type of enemy have 25 times the HP of another. If Kobolds deal 1 damage, that means that Adult Dragons have to deal 25 damage (on average) (orcs deal about 5, so, 1d10, or 1d6+2, or the like). On the other hand, if we want even Kobolds to deal variable damage, then we have to have them deal at minimum 1d4. This means that orcs would have to deal the equivalent of 5d4, and Adult Dragons 25d4 damage! We're at first level, and we're already throwing 25 dice? Of course, the raw dice problem can be easily avoided by simply using static values (for instance: 5d4+50), but this means that the variability of the dice becomes massively less significant for higher level threats.
What's more crucial is that, we're still at the lowest level scale. We know, for instance, that Orcs will eventually become the new kobolds-which means it's necessarily true that Adult Dragons will become the new orcs, and SOMETHING will become the new Adult Dragons. This something (We'll call them "Wyrms") will have damage scaling of 125 times the damage of kobolds.
Now, you can reduce this problem by eliminating kobolds entirely-let's say there's no monster on earth that's weaker than an orc. Okay, so now our wyrms-which you're not expected to face until you're well into the game (how well into it? Beats me)-only deal 25 times our atomic value. However, since Orcs are 1 PC threats, we presume we want them to deal more than 1 damage per hit, so that's still 50+ damage.
The other question is, how many adult dragons equals a Tarrasque? If we assume a Tarrasque is "worth" the same as a single Wyrm, then that means that the answer is five-and only 25 orcs. Somehow, I can't see the Tarrasque being taken down by anything less than a massive army. So we can pretty much assume there's at least one more level of scale beyond wyrms-so instead of a scale of 25 orcs (or 125 kobolds), we're left with a scale of 125 orcs (or 625 kobolds!)
Now, the fact that a monster is worth hundreds of times the damage of another monster is only a problem if we're talking extremely high damage values (moreover, it's a problem if we realize "how are we going to get PC HP to scale like that?") What is almost certainly going to happen is that damage will be measured by "After Resistance" damage values. Imagine armor that absorbs damage, rather than just sets your AC (sacriledge in Dungeons and Dragons I know, but I'm trying to give this system the benefit of the doubt). So, an orc may always deal 5 damage, but then your resistance reduces that to four at the same time that your net total HP has doubled, meaning that the percentage of HP is roughly 1/5. It's impossible to really say without the specifics-but if you want to avoid exponential HP, you need to have a resistance value that will, eventually (probably not quickly, but eventually)-reduce enemy damage to 0.
My own fears are more along the lines that a Tarrasque won't be "worth" enough orcs. Because epic level play has always been problematic, I suspect there will be a push to more "traditional" gaming-which I've always seen means low level grinds. And if we're talking low level, we're generally not talking about a need for monsters that can single handedly take out entire armies.