Some general rules (or at least requests):
1. If you don't want an alternative to fast travel, please don't post here. You already have what you want, there is no reason to troll people who are saying what they want.
2. If someone is posting here saying that Fast Travel is fine the way it is or is flaming/trolling, please do your best to just ignore them.
3. We cannot predict the functionality of the new engine, so any examples will most likely relate to the Gamebryo Engine. I am an experienced Oblivion modder, so it is all based on how fast I can do things. It is faster then a person new to modding and not as fast as someone who made the game.
What Exactly do we Want?
A Toggle Option for Fast Travel (Like I said, we don't want it gone)
Travel Alternatives at Major Cities (Caravan guides, mage guild portals, etc.)
Mark and Recall
In-depth Looks at our Wants
Toggle Option
There have been many mods that remove Fast Travel from Oblivion and Fallout 3. The mods that do this are small, less than 10 KB. That is less than 1/100 of a percent of a standard DVD. Most DVDs used for games are Dual Layered, which means it has about twice as much space as a standard DVD. Granted, making it a toggle option would take up a bit more space but from my (albeit minimal) experience in building menus in games and applications it would in no way be large enough or take long enough to detract from any other gameplay elements. This is the kind of thing that is made in an hour or two.
Travel Alternatives
This would take a bit more than making a Fast Travel Toggle Option. Depending on how it is done it could take minimal resources or quite a few resources. Let's anolyze the options I listed above:
Caravan Guide - An NPC for each city which takes a few minutes to create, clothe, and put in the game world per NPC. A faction or some way to determine what NPCs offer travel services so guards aren't accidentally hirable. That is another minute. Putting a simple quest that gives the NPCs dialog and then giving the PC options to respond based on where he is and how much money he has. This would take another 10 minutes. The longest part would be getting the dialog voiced by each of the proper voice actors. That would be the longest and most expensive part.
Mage Guild Portals - First things first would be making a model. I haven't done any modelling myself so I can't give an accurate estimate here. I would have to say the model and textures in the hands of a pro would take a few hours. From there it is easy. A simple script that asks you what guild you want to go to takes a few minutes.
Mark and Recall
The easiest choice to make.You make an invisible marker for the "Mark", then you give a spell a script effect, an example of which is in the code tag below. Then you either make it a starting spell or put it in a spell vendor's inventory. 5 minutes.
scn MarkAndRecallshort ChoiceBegin ScriptEffectStartMessagebox "Do you want to travel to your Mark or set a new Mark?", "Travel to Mark", "Set New Mark", "Cancel"Set Choice to GetButtonPressedIf Choice == 0player.MoveTo MarkRecallMarkerElseIf Choice == 1MarkRecallMarker.MoveTo playerElseIf Choice == 2ReturnEndIfEnd
That is the summary of at least my thoughts on this issue. Feel free to voice support, share ideas, etc.