1. None of these have any significant downsides. They're also either way over the top(the first one), or already exist (last zanba = chain sawd, invisibility cloak = kroe's sweater), or are just plain bad (elemental ring; not at all useless, it's way brokenly OP, poor design, and a ripoff of another servers' item). We can't really do negatives quite like that either. Even if it were possible, it would lead to inherently bad design as any possible downsides would easily be mitigated by other factors, and you would just be left with a way too big a power creep on items (even if they were situational only). Better but with a downside isn't always a principle that works well in practice, but especially so in this particular game.
2. Isn't the very first thing you suggested a charge weapon? Also we've only ever added 2 charge weapons I think. First was in valentines 2015 (Slicer of Vengeance), and we just got the second one (Fury of the Beast) more than two years later. It's not like we're doing it very much.
3. Several things have been made that have a decent grind. Fury of the Beast, Crush Cannon, Sil Dragon Slayer, Blood Tornado, Crimson Sword, Macho Blades all have multiple dozens of grind potential (even inferno girasole has +20), and we've increased grind limit on several other vanilla weapons like dual birds, rambling may, and angel harp by significant amounts. There isn't a lack of grinding overall for new items.
4. We already do tons of combinations, probably more than we should even. From Halloween until now, we've added EIGHTEEN combined items and five non-combination items (not including the three new units, since units aren't ever combination). I don't understand how much more you think we could do. Not everything can or should be combination.
5. I can't make Claws or Launchers not suck by inherent design. I would never give any weapon, regardless of type, 2000atp, that is just silly. The katana example is suggesting to make Raikiri significantly stronger than Orotiagito and give it more than twice as much ata as any vanilla item and still not describing a significant downside; regardless of the numbers, the design really wouldn't fit in well either. I've also only added 1 mechgun personally (the first new mechgun since Psycho Raven was added back in 2013 ), and it's a very useful one that fills a really nice role; I do not regret a single thing about Rage de Glace. The same can be said about Kajex's new Samba Fiesta. Both of these have very specific class limitations and fill specific roles for those classes. Again, it's not like we're doing mechs very much.
I'm sorry, but I don't think there is anything here that provides something even "partially" usable really.