I just made it through Elantris for my second time (first time through after other Cosmere related stories) although I haven't read through any annotations or many WoB's from Elantris. Just wanted to put some of my thoughts out even though I am sure all or most have probably been discussed thoroughly given how long Elantris has been out without receiving an incredible amount of additional material to go off of.
Sel-based magic as a whole seems to be granted to individuals that are incredibly devoted to something. Their access to the Dor seems to then be determined by the land/region they most identify with (AonDor for Arelon, Dakhor for Fjorden, etc.). We see Shuden, who appears completely normal, use ChayShan and appear to have a glowing effect while using it (from accessing the Dor). Dilaf also appears normal while clothed, but has shapes in his bones, and has a glowing effect when accessing the power granted to him from Dakhor.
While I've been lurking around this forum I have seen it posted before that AonDor can be thought of similar to a programming language. Having that in mind during my second read made me think of the Elantrians in a very similar way to characters from another book, Off to be the Wizard. To summarize what I see as similarities from Off to be the Wizard, a group of characters find a "program of the universe" if you will. They then create their own functions within this program to perform preset actions which would essentially be magic. The group sets up specific identifiers within the program to only allow people that meet certain criteria (specific individuals that must be carrying a staff of certain length and wearing a hat and robe of specific dimensions) to run their unique functions. I couldn't stop thinking that Elantris worked in a similar way. Before the existence of the city, I would think that anybody from Arelon with access to the Dor would also appear completely normal unless the Dor was actively being used. Aons were probably not particularly strong so some well informed practitioners decided to make a set of incredibly large (and essentially permanent) Aons to boost their power and provide other desired effects.
Elantris seems to be a set of Aons targeted only at individuals that meet certain criteria (access to the Dor and have a connection to Arelon) that increases the power of their Aons and (I assume) gives them their quicker healing, agelessness, etc. The extra healing/agelessness given by the Elantris Aons are what I believe gives the Elantrians their constant glowing from the Dor actively effecting them. From the story about Dilaf's wife, it seems that when an Aon that is targeted at a person goes wrong, it gives the same effect as the Reod. This leads to thinking that all Elantrians appear as they do because the entire set of Elantris Aons that are targeted at them are incorrect (because of the missing chasm line). What isn't really answered though, is why an incomplete targeted Aon traps the recipient in the Reod state. How can they continue to function, almost normally, without food, breathing, etc? Also, why does (seemingly) only Raoden experience the waves of AonDor pushing against him internally until he completes his first functional Aon?
The various types of access to the Dor seem to be partially or fully region-locked on Sel. AonDor is weaker as the user is further from Elantris, and I believe a WoB said that Forgeries stop working if moved sufficiently far away. Without more source material it's a bit hard to determine the drop-off effects of each system. AonDor was weaker in Teod but is it actually just the normal strength of AonDor without the boost from Elantris? The Aons drawn in Teod are weaker but what about any other possible effects added from Elantris (we don't see Raoden stop glowing there)? When the Dakhor monks are revealed they seem to have the same power regardless of location, and ChayShan is still very powerful in Teod. Does the region-locking of Sel magic have to do with regional ideas/culture as well and not just location in the world? Do Dakhor powers continue to work because the shapes are formed in the bones themselves, or because Fjorden culture may see all the land as theirs and that it is just currently occupied by heretics, or because Derethi efforts are not only aligned with Devotion but with Dominion as well? I don't see why the land itself would make a difference to the Dor unless it is based on how the people as a whole view that land.
I can't wait for more stories to come out that take place on Sel. It will be interesting to find out more of the inner workings of the Dor and begin to see how that may shape the Cosmere events in the future. Any feedback, clarifications, or other discussion would be appreciated!