I don't agree with Chain Specials. Its an ability that's 100% universal and not learned naturally. It also leads to massive arguments as we've seen in chat people have claimed some combos are viable while others have different experiences with them (Like someone claiming Crimson Squall chains perfectly with itself, when several people have had experiences (including myself) claiming it very much DOES NOT), especially since some characters like Reimi require massively on ranged aspects that can completely change the viability of those combos. This isn't like SO3 where Chaining is an innate feature; you can only chain when you gain the ability, which is something every character gets *AND* gains through non-natural/plot means, which is to say, goes against the very nature of the DL (unqiue, natural, or plot given skills only, in short.)
And it doesn't really reflect in game use that much. Consider the differences between SO3 and SO4 for a moment:
SO3, there was the Fury system. A character had a restriction of how many moves they can chain together, and what not. As a result, the amount moves would chain would also vary in addition to the damage boost. Fayt being able to only go like Side Kick -> Ethereal Blast for example was a flaw for him, where as Maria could chain together like 6 Scatter Beams or whatever, for good damage off a basic move. Furthermore, moves like Dimension Door and Vampiric Flash exist; the "Continuals" where you can up its damage by increasing the duration of the move, but it drains more Fury the longer the moves duration. It was a far different system, and not only was Chaining 100% innate, every character functioned with it differently.
SO4? Everyone can go Physical -> 6 Specials. There's no restriction barring MP here, and I don't think that's going to matter much in the DL. Everyone benefits in the EXACT SAME WAY here, unlike SO3, so really it just goes into a debatable field of "what moves are most viable to chain together!?!?" In game, furthermore, it was important for how often you can keep an enemy tied up (until they used Rush *shakes fist*), something that, again, does not apply to the DL. Its not unique in the slightest, and not naturally gained, and it doesn't actually reflect in game usage that much, cause everyone can use it the same way.
So yeah, I honestly think Chain Combos are 100% "no" in the DL.
For skills...2 users at most. This is the standard for a cast about the size of SO4's. I don't know what this allows, but No to any skill usable by more than 2 PCs...
EXCEPTION: Faize and Arumat.
If there are 3 users of a skill, and 2 of them are Faize and Arumat, I'd still allow it. IIRC, all of Faize's skills go to Arumat anyway, and the two are never in the team together, so yeah, for the purposes of skills, I'd treat them as the same character. So if we have 3 users, and Faize and Arumat are two of them, I'd still be cool with allowing it.
The Creation thing?
I think SO2 dealt with this before, and it was agreed No. Just cause a character can create an item doesn't mean they should be allowed to use it. I seem to recall a few items in SO2 can only be created by a specific character or two, and as a result, would be the same deal. Its basically giving them a DL advantage they clearly don't have in game, reason being everyone can take advantage of that object Meracle creates. She creates it, but it still goes to the party's inventory, and you can hand it to Lymle (assuming she can equip it) just as easily as you can hand it to Meracle.
