I know that this is a long shot, but would it be possible for a standardized framework for modders of TES 1:Arena and TES 2: Daggerfall, to make modding more common and easier?

Well, in both cases of course it's possible, just depends on if people actually want/have the time to work on it. Modding the older games is always going tob be more complicated due to the lack of official tools and the fact that Bethesda lost the source code for both games. In spite of this, Daggerfall has an (as far as I know) active project called Daggerfall Tools For Unity, which is an attempt at replicating the original game engine in Unity (the same engine that powers basically every 3D indie game nowadays), with a focus on modding tools. I'm also going to go out on a limb and say it's unlikely that Arena's ever going to get enough interest to have mod support thanks to the microscopic fanbase and the way that the game engine is effectively just a simpler version of Daggerfall's.