1. Which one is better for modding?
2. Will it ever receive the modding support Skyrim received?
3. Does SE have all the DLCs included in it?
4. After SKSE is out, will original Skyrim's mods work with the Special Edition?
5. Apart from retextures, are there any storyline or dialogue or any other differences in both the games?
For me right now, neither. I have played original + DLCs back and forth enough that it completely lacks any replay value for me, what made it fun and replayable are the mods that alter or add quest lines, especially adult focused etc. On the graphical end I can't play it without high res textures, fully functional vag, HDT style bouncing bodies etc.
I care nothing for leaves, terrain and all that, all the ENBs, fog, light effects and all that I used in order to have better visuals and overall better graphical functionality on player and NPC bodies, not things such as junk objects or terrain.
Add to that, I took the plunge and left Win 7 64 completely behind and switched entirely to Win 10 along with a whole new rig. Under Win 10 original skyrim is limited to 4 gigs and with my mods I hit that limit very fast. Because of this and the fact that its too much of a hassle and drag to upkeep a seperate drive with Win 7 on it just for Skyrim, the original game is just unplayable, completely not worth playing.
SSE gives me the memory and far superior stability to run everything, but there is nothing available yet that I actually want to run with it. Only things I have found interesting so far are some outfits, but even then it just doesn't hold my interests because of lack of bounce and lack of other main mods to use those with. There are some exceptions and workarounds for some things, but they feel either very partial and incomplete or are too much of a hassle for me to use. I don't get the whole conversion things and all that since I am not an IT person or mod designer, no matter how many guides I follow, always some issues that I am unable to resolve within a reasonable timeframe, thus making them unusable.
SKSE64 will change this, but then there is also the timeline to convert / re-develop mods for it, and I am not sure that by then I will still be interested in Skyrim or have the time to devote to modding and playing it.
So I kinda gave up on both of them, though I do check on how things are progressing (hence I am here) and depending on the timeframe when things for SSE become available, I might or might not come back to it.