@Wenceslaus
I don’t have time to write a monster reply right now, so please read what I’ve written previously (in this thread).
Here are a few quick points though:
Two separate systems - Everything will need to be considered from both view points from now on. It’s no longer good enough to just work well from first person. A quick example: sword fighting from first person without a HUD would be a possibility as it’s much easier to see the direction of the enemy’s blade. Archery also needs no HUD from first person. Maybe Warhorse wouldn’t want to go HUD-less, but if they did want to, gameplay-wise, they have the option to do so when only considering the first person viewpoint. Again, if the game were only third person, a HUD-less health system of blood on the character or via animations can be used; this wouldn’t work for first person however, so either you need to do twice the amount of work or come up with a compromise solution which is often less ideal than the camera specific one and takes more time out of the design and testing budgets. These are just a couple of HUD only example, the same applies to all elements of the game.
Balancing combat and stealth - In third person you can see behind you, giving an unrealistic degree of situational awareness. Regardless as to whether you prefer this or not, it’s very different to what you see from first person. This will change how difficult the combat is and again means it has to be balanced for two separate systems, or a compromise reached for both. From TPV, you can ‘look’ around corners (cheating with the camera), whereas first person requires a proper lean system and completely changes the feel of the stealth mechanics.
Camera specific options - I’d like to see helmets obscure the view in first person and sounds become muffled and exaggerated. This isn’t just more immersive, but has large gameplay implications; you’ve better protected, but have far less situational awareness. Imagine wearing a full suit of armour in a rainstorm, the reduced visibility through the visor and the loud sounds of the raindrops on the helmet. Pop into TPV and it’s a totally different experience. Having a third person option mucks this up (both restricted view and sound effects) and again means two separate systems which both need testing. This isn’t just visual and aural, but affects gameplay as well. (EDIT: Another example, akin to that of the helmet visibility, would be blocking with a large shield obscuring your view from first person, but not at all from third)
Fall back option - Some things are hard to get right from first person, such as horse riding. With a third person view available as an option there will be the temptation to skim over difficult areas and fall back to the third person ‘default’ riding view as is done in many games. I don’t want to see this. I don’t want more external cameras for my racing game, I want an improved first person system.
Collision and camera clipping - There will be issues with collision; as Dan mentioned interiors can be a problem and are often made over-sized for third person games. He said that first person might be forced on in interiors as a solution, but then you have an awkward system which allows TPV in combat in some places, but not in others etc. Some people will moan about this and dev time will no doubt be spent seeing how hard it would be to implement. I’d rather that time was spent on other things.
Again with the clipping issues - Regardless of whether TPV is denied for interiors, there will be some issues in exterior locations too. This will again eat into dev time, either through more coding or artists having to setup specific camera collision meshes.
Better experience from a single viewpoint - You can make a better, ‘purer’ experience when you’re tailoring it to just one viewpoint IMO. All the things mentioned above can dramatically change the way the game feels and is played, but by having to make both views work you muddy the water and exclude the possibility of certain gameplay elements which would only work from one viewpoint.
There are other reasons too, but I’m too busy right now to go on. Already written too much as is - So much for a ‘quick’ reply! :).