"Why is this 4D Wheel Banned?"
Big Bang: Big Bang is hilariously broken in limited, it weights about 42g plus a clear wheel (more than Libra) and its shape makes it extremely effective for attack and anti-attack generally in a single combination.
Fang: Counter Mode knocks out the entire format without breaking a sweat - Fang was quite possibly the best attack wheel available at the time it was released, after all.
L-Drago Destroy: LDD is definitely one of the less worrying 4D wheels without BD145/SA165 or RDF available to it – without LDD's weight being necessary Lightning is scarier offensively and despite its massive 44g weight, LDD Spin Stealers are easily handled by Libra Anti Attack (at least in LDD B: D vs MF-H Libra GB145RF). However, F230CF/GCF as well as various other CF/GCF/XF/WF and Anti-Attack setups would need to be tested for it to be unbanned and even then, I'm not sure it would be healthy for the format – and if Libra is ever banned (which hopefully won't be necessary) then LDD should be illegal too, as then its weight advantage does become a bit of a problem for the rest of the format. Still, perhaps something to consider/look into in future.
L-Drago Guardian: Everyone that said "oh LDG and LDD are basically the same wheel" should compare them in limited. LDG's huge defensive superiority over its little brother becomes strikingly obvious, and for Defense and Spin Stealing and probably also Anti Attack, LDG absolutely dominates, and I'd hate to see what LDG F230GCF is capable of doing to Limited.
Kreis: Despite being the embodiment of mediocrity in standard, Kreis is an absolute monster in Limited, with an 8g weight advantage over everything but Libra. In Stamina mode, it's basically immovable on standard defense setups, while in Attack Mode, MF-H Kreis Aquario CH120RF is capable of KOing 145-height defense with ease.
Beat: Personally, I've always found both incarnations of Beat far too inconsistent to actually be effective attack wheels, but judging from the results others have got with the Metal Fury version, odds are this is just an incompatibility between the blader and the blade, and Beat is broken as heck by means of knocking out the whole format.
Hell: This was mostly because of MF-H Hell Kerbecs 230CS, but then I'm not sure if that's too much stronger than other 230CS combos any more. However, specific attack combos (MF Hell Kerbecs CH120RF, Hell Aquario H145RF) are able to KO the entire format, so Hell would dominate attack, be a major balance part (as 230CS is far from the only setup it works in) and overshadow a lot of stamina types too. I do have to say that I think it would be healthier for the format than Metal Fury Scythe is (heck, even having the both of them together would be better than just having Scythe), just because it's offensive rather than defensive.
Fusion: While it hasn't been tested in Limited, at 44g before a clear wheel (so ~47g with one), Fusion is a whopping 10g heavier than every other legal wheel aside from Libra (and soon, Omega), and the one combo that it found use in that I remember was a Defense custom. It's therefore probably safe to assume it's going to be way too strong defensively for Limited.
Jade: Jade probably deserves being tested. It was banned as a precaution (and for the convenient "all 4D are banned, which is about to go out the window with Omega), as with a 3 gram clear wheel it's slightly heavier than Libra, which is already one of the strongest wheels in the format, and it is generally defensive which is a risk for a significant portion of the format's wheels.
If someone wants to test it, Defense, Anti-Attack and maybe some cursory attack and stamina tests (unless it's completely awful at them, in which case those two could probably be skipped) would be needed, but to be honest given it's kinda a defensive wheel it is probably not what the format needs right now.
And the stuff that saw significant use in Standard in setups that translate easily to Limited:
Duo/Death: Both are immovable by and able to OS the whole format.
Basalt/Diablo/Wing: Their weight means the entire format bounces off them as defense combos. Basalt and Diablo are both able to KO basically the whole format in Attack, while Wing LTDC are particularly hard to budge.
Variares/Blitz/Flash: Able to KO the entire format with ease (even MY variares!)
Phantom/Scythe: Both Wheels' combination of Attack, Stamina and Weight make them far too powerful for limited. Scythe is also ridiculously good at Low Track Defense.