I am one of those "old" guys who doesn't have the reflexes to keep up with you youngsters. :-)
Ideally, I'd rather rely upon skill, but in a PvP style game, I'm at a real disadvantage. If a mod might help me be competitive, it could be the difference between my being a liability to or a contributor to the group effort. That said, if the elite players (and I'm not using that term negatively, but as a recognition that many of you are extremely skilled at these games) won't snipe at those of us with less ability about "not pulling our weight" or holding back the group because we can't perform at the same level as you, then we old, slow guys would have no reason to want or need the crutch of a mod. If, however, I am going to be subjected to criticism (actual or implied) or be left out because I'm not as good as the best--then I am more or less forced to try anything that might give me a chance--after all, I am paying to play the game and it is the direction the Guild is going, whether I like it or not.
I ran into to elite players looking down on those who weren't up to their standards repeatedly in WOW--everything was measured by the DPS meter and the difference in a keystroke pressed a half second too late could be enough to make your DPS fall below what was acceptable to some people. When that happened, I found that I wasn't accepted or wanted for raids except when no one else was available. Consequently my raid experience and my gear was always less than most of the others. It becomes a snowball effect and I found it impossible to catch-up or keep up until I got in with the right guild that practiced player development, helped me learn, would make runs especially for the lesser experienced and lesser-geared members solely to help build-up the available pool of guild members who would contribute. In that case, the PEOPLE in the guild replaced the need for the artificial assistance afforded by MODS. I would suggest that the same principle would apply in ESO--the need for MODS is more likely to be dictated by the attitudes of the players one is associated with rather than the actual efficacy of the MOD itself.
I am concerned that in a game where published rankings are an official part of the game, a situation will develop--as it did in WOW--where a relatively few, highly skilled players, will constitute a de facto "upper class" and the rest of us become relegated to a lower class whose play and participation choices are limited because we can't meet certain minimum standards of performance. In that case, if combat mods can alleviate that situation, then I am for them. The skilled players who don't need them, don't have to use them and should actually welcome the fact that using combat mods might make fewer players a liability. However, I can certainly understand the resistance of skilled players to mods if those mods enable lesser-skilled players to out-compete those who don't use them, but would otherwise be superior. It becomes something like the discussion regarding performance enhancing drugs in pro sports: the best don't need them to be the best, but if the rest use them, then the best have no other choice to do likewise in order to remain the best. Unfortunately, any competitive game or sport will necessarily foster that type of situation. If ESO, by design, wants to create a competitive situation through rankings, but retain as many paying players as possible, then it behooves them to design a system that rewards superior players without also penalizing the average player. That is difficult to do. It many end-up that MODs are the only way some players can remain viable in the game and if both ESO and Gaiscioch want to keep player/members, then they will have to make it possible for the average, but paying, player to be able to play "when they want, as they want" even if that play style does not necessarily meet the standards of the elite or highly competitive.
That said, I really enjoyed most of the non-combat related MODs that assisted in navigation, communication, and organization of in-game WOW gear, etc. Raidcall is, in effect, a MOD in the sense that it improves on the in-game communication, even if it doesn't actually modify or add to the game client programming itself. From that standpoint, I would vote for allowing the API to accept MODs, even if they were limited to non-combat MODs only.