- replacing the Readiness DCs with the standard tier-based 13th Age DCs
- adjusting the max distance per 1 day turn to better reflect my real-world experience as a backpacker (increasing mileage)
- requiring an Int check for mapmaking to grant the navigator a -5 to the DC
- clarifying Searching as an umbrella term for hunting, tracking, exploring, etc.
- adding the option to make a Con OR Wis check when attempting multiple actions (depending on the nature of the second action)
- and finally adding a d8 roll to determine random encounter difficult in lieu of a specific wandering monster chart (1-2 is an easy encounter, 7-8 is probably too tough to take on, and the rest is a balanced encounter).
It's tough for me to not reflexively compare these exploration rules with the Journey rules from The One Ring, which I purchased a little over a year ago. Those rules are probably the most well-designed of any exploration mechanic that I've encountered in a tabletop RPG. One of my favorite aspects of these rules is how well they balances light and heavy armor. A character with a high Fatigue rating can be made Weary very quickly, and that results in a significant decrease in overall effectiveness. In short, it definitely pays to travel light, with lighter armor having an edge unless you're defending a fortified location (and thus unlikely to accumulate travel Fatigue, and with ample opportunity to get bed rest).
Unfortunately, there's really not a good way to replicate that in D&D. Part of the reason why this works is that heavy armor in TOR just gives you more protection against Wounds, with most hits simply dealing Endurance damage. Your stance also determines how hard you are to hit; a lightly armored character in defensive stance can be pretty hard to touch most of the time, even if he is susceptible to a lucky hit.
In D&D your AC is just your AC, and based on whether you're expected to be in melee combat it's usually assumed to be a certain value. Case in point is Barbarians, who don't wear heavy armor, instead having a class feature that buffs up their AC roughly to parity. Tweaking with armor can throw combat assumptions really out of whack. It's also tougher to emulate Weary as presented in TOR; ignoring low rolls out of a dice pool still allows a lucky character to function at full effectiveness, whereas numeric penalties don't accomplish this. Instead of simply being less likely to succeed, your ceiling actually drops.
Finally, the hardships of the journey simply isn't a major focus of D&D. TOR has those mechanics because it's a huge theme in Tolkien's works. A huge theme in D&D is looting. Fatigue would work inconsistently in such a system by punishing it early on, making it trivial once you grab yourself a Bag of Holding, and punishing those classes who need to wear heavy armor in order to be effective.
That said, while the existing mechanics don't offer any obvious suggestion for a Fatigue system, I wouldn't mind an optional module being offered as part of an "advanced" exploration package.
Despite these rules lacking my favorite feature from TOR, I do really like them. One thing they do better than TOR is emphasize navigation in a more structured way. The d4 roll is a simple and effective way of adjudicating how lost a party gets, and the tradeoffs of the different Travel Paces give the players a lot to consider. Though I usually don't bother in my games, tracking Rations would be desirable to generate enough pressure to temp players into choosing faster paces. Encounters that deplete rations (They got spoiled in a swamp! Raccoons rifled through your packs at night!) likewise have more of an impact, perhaps being enough to completely change the goals of the PCs. Even without Rations though, Wandering Monsters might be enough of an impetus to travel quickly, especially in dangerous areas. The more quickly you cover a given distance, the fewer encounters you'll generate.
The granularity in the time scale is a nice touch, and feels like a logical expansion of the 6 second combat turn. It provides enough structure for long-distance exploration to provide meaningful choice without being too stifling. It's tough to wing it for things like travel pace, and usually my players will say something to the effect of "I'm going as fast as I reasonably can while still doing X." Great, but without a baseline I'm forced to improvise, and the players usually try to tweak their wording to get more of a benefit or eliminate tradeoffs. I think these exploration rules hit the sweet spot in codifying that baseline enough to generate predictable results and provide meaningful choices, all without being too crunchy to become unwieldy or to stifle flexibility.
Finally, the very existence of these rules - the fact that space was dedicated to exploration - is a signal to players that it won't be a waste to invest in it, and more importantly gets them thinking about it ahead of time. On the other side of the screen, because they're there, written down, DMs might be more likely to put some focus on exploration. Sometimes "it takes you 3 days to get there" just isn't very satisfying.