I would not use an automatic solder feed. The feed rate, diameter and positioning of solder is something that I vary under fingertip control for every solder joint I make so I can't imagine a satisfactory automatic setup.
The pencil type iron is so very familiar and has been the main-stay for so long that many, like me, will respond that they simply don't want to change. The issues that I have with various models include:
- pen-holder (the place where you park the iron when not in use) moves around the bench too much. Needs to be anchored in place, or weighted to avoid movement. Most irons have fixed this I think, just not mine.
- the insulator that keeps heat from my hand tends to slip down the iron too easily. It should remain in place.
- some irons are too fat and hard to hold (metcal comes to mind) while others are fine (weller).
- I wish I had a hot air pencil as good as the old Hakko I used to use. (off topic, I know)
- I solder 99% of the time under a microscope and when working on 0402 SMD parts and fine pitch leads, any shaking of the hand becomes a problem (and I'm not getting any younger!). So I solder by keeping the heal or side of my hand on the bench and pivoting on that point with the pencil. I can't imagine doing this effectively with a pistol grip design. I think it helps a lot to have the first (pointing) finger out straight for better stability or rather, directly opposing the thumb in the classic pencil grip. A pistol grip would occupy the first finger holding a trigger and you wouldn't be able to stabilize this way. The diameter of the pencil and the weight of the pencil should be as small as possible to facilitate this.
- I don't have any complaints about tip interchangeablility as I tend to maintain three irons on my bench, a fine tip, a medium-fine tip, and a large tip. And in case of really big stuff, the gun or bar iron comes out. So I'm not changing tips all that often anyways. This points out that any iron should be small enough so that you can have at least two on the bench without taking up much space, and preferably three.
- you might consider combining a hot air pencil into the design too, but on the other hand I really hate it when an iron station becomes large and uses up critical bench space. I've got two of the those all-in-one solder/hotair/desolder/vacuum stations in addition to my irons and they are a pain in the neck most of the time because they are too big.