Something like this was in Daggerfall. It really suited that game due to the immense size of the landmass. In Skyrim, it may be a bit lost though. I wouldn't expect it to take more then a few days to walk from one end of Skyrim to the other, so planning out the travel speed, where to rest, etc., may be a little unnecessary. Although it does make me think of a fast travel option that can please both parties
Yes, Daggerfall suited "better", but there are many mechanics to make a trip last longer:
* No regen. Could be an issue for those manually traveling and relying on feather spell.
* Have a cart or a cart and a horse to carry loot? Your speed is lowered, but you can carry loot.
* Need for nutrition. There can be areas where this is low access, slowing you down.
* Potions to compensate? Sure, but that would then be the cost.
* Maybe bandits are hyperactive at night? Better travel only during daytime.
* Services only open for certain times a week and only a couple of runs each day?
* Mages guilds (extremely convenient due cities), require someone to push the buttons. So, delay for night.
* Propylon you first have to find. Once you do, nice alternative.
* Avalanches blocking the way. Probably hard for a dilligence service to get through.
The point is, by doing it fully manually (like today NOT using fast travel), the price is the workload required, the tediousness of doing so, but the big reward is less time goes by in the game world.
Using "Fast Travel" in the game (depending on options), will be far less tedious to do and quicker to perform in the real world, but the price to pay is that more time will pass by in the game world.
Interface:
Unlike Morrowind where the player had to take notes on where everything went and at what times, this should be accounted for and shown directly on screen for the character. Once he know that Town A is connected to Town B via boats or dilligence (and that route has been cleared of bandits or whatever), that route will be selected and shown automatically on the map, depending on travel settings naturally.
Hovering over a location you've visited before, game will depict the route coded with means of travel. Going from your current location to another may involve:
* Walking from current location to nearest stable.
* Dilligence from stable to town A.
* Dilligence from town A to town B, but since it's not in you'll have to wait a day there.
* Walk from town B to town C, since settings dictate you want to go as fast as possible, waiting is this time slower than walking, and you're ok with some risk.
* Walk from town C to destination, as there are no services for this portion.
Red route shown (highlighted road) for risky parts of the route, like walking.
Green route shown (highlighted road) for safe parts of the route, like travel services.
Blue route shown for travel across ocean
Yellow route shown (curved arrow not on roads) for teleportation based distances, like mage teleportation.
I'm seeing a problem though if we have Dilligence based travel and Mages guild travel, if everything is present in the same towns, as they make eachother completely redundant. So maybe instead of Mages guild based teleportation, we get back witch covens which offer these kinds of services? Dunno, just throwing in wild ideas here