I recently answered a question on a luthier forum about neck width and string spacing, specifically about doing a dreadnought body with a nut matching a classical guitar width.
I have done some wider nuts on electrics to allow for easier fingerpicking, although not as wide as a standard classical style guitar. There should be no issue for a dreadnought body with that width of nut. Too much wider than a classical string spacing might call for a change in bracing away from that of a standard six string, but a quick search will show many varieties of guitar with wider necks, including additional strings. Of course the bridge spacing and neck width/taper have to be designed accordingly, but that is a given anytime you change dimensions on a plan.
Concerns if you tried a wider (or smaller) than standard nut on an electric would be the strings going wider at the nut than at the bridge (unless you make your own, there are two standard widths for six string electric guitar bridges) and going wide (or narrow) over the pickup poles. There are standard, f-spaced humbucking, and trembucking pickups for the bridge due to the difference in bridge and nut spacing of the two major guitar designs. Single coils can be set at an angle for narrow string spacing and they are angled on F-style guitars. Scale length and pickup position also decide the string spread at a given point. A standard humbucker near the bridge on an F-spaced or vibrato equipped guitar will have the e strings wide of the poles. Visually noticeable and debatably affecting tone. Here is an article by someone who is a bit of an expert if you want to learn more: Lollar guitars pole piece spacing.
You could of course design your own bridge and use pickups that have blades instead of individual pole pieces which allows for more variation of string spacing without the pole spacing concerns. Of course you should layout any design that is not standard before building, as the neck width and taper are affected by the nut width, bridge spacing, and scale length.
Part two of the original question. I mentioned that there are two popular ways to space the strings on the nut, one is using a special ruler or use a computer app to get equal distance between the strings which assumes a certain guage and looks aesthetically pleasing. The other is to measure in an equal distance from the edge of the fingerboard and then use dividers to mark out equal spaces for the string centers.
A response after mine was given that they should be equally spaced between strings and that the sides should be half the outer string spaces, and therefore the guages must be known and not changed because it would throw the whole thing off. They made an ascii graphic similar to this: |||—||—||—|—|—| No one disputed it and I didn’t see the response until much later, making it an old thread, so I refrained from further comment. I am not trying to say that person is wrong, obviously enough people use that method or similar that there are apps and special rulers made by reputable luthier supply shops for that purpose. But….
Above is my ultra fancy and not accurately scaled or proportioned drawing to help illustrate reasons why I do equal spacing. Here are my reasons beyond just that I was taught by respectable luthiers to do it that way.
1. You play by fingering the top of the string, not between the strings. In this case I think feel is more important than aesthetics.
2. Pickup pole pieces and bridge saddles are equally spaced and to get straight string pull through the headstock I use equal spacing on the tuners. Basically all the rest of the guitar uses it. Equal space between strings would mess up this straight string path.
3. I have successfully changed string gauges on most guitars without issue. With the equal space between strings, changing gages would require changing nuts as it is spaced for a specific guage?
4. Equal space from the edge of the fingerboard gives consistent feel and no fear off pulling string off the edge. The half the distance of the outer string spacing method leaves uneven widths (see bottom of my graphic above) and if exaggerated could be enough to leave the string too close or very far from the edge.
At the end of the day I must admit I have not tried a guitar with equal space between the strings and it could be great. Or not noticeably different. Always happy to hear anyone else’s opinions if you care to comment.