1. Since the conversion of the old armor kits to the new system doesn't seem to make any progress (at least from a players point of view)... if it really takes that much effor to convert it how about some kind of poll, which of the missing armor kits people want to be added next and you just pick the first 1-2 from the list for every new update? (and I really mean update not patch) Or you could just use the sales history which of the missing armor kits were the most wanted ones, maybe you are doing that already.
The main thing of this proposal is that it seems Turbine needs some kind of fixed plan to convert the old armor kits or no one is going to work on it.
I know this would take some time till every old armor kit gets converted but it's far better than the current situation. And if you still don't know an exact date when the next batch of armor kits are going to come to the store it's probably not coming with U20. And U21 is probably going to come nearly one year after the introduction of the new cosmetic armors. And this doesn't look very promising to see any of the old kits getting converted, even if it's still intended to be done somewhen.
2. Another option, if you really have problems getting this conversions done (having time to get this done)... how about giving us the old armor kits back until they are converted to the new system? I know the first weeks of the new cosmetic armors there were still the old armor kits in store so one could still buy the old ones. But since nonone told the players it would take you months (or even years if you don't know when you are going to continue the conversion) to get all old armor kits back (or don't even convert really all old armor kits) most people didn't know there was any need to still buy the old armor kits. If someone would have done, I would have at least 3 kinds of my prefered armor kits in the bank now (at least on my main characters). :S
It's just that I am very sure most people who care about the old armor kits would like to see some kind of progress instead of waiting for an update in the undefined future which hopefully includes all missing armor kits at once (and I somehow doubt this would happen anyways). And every new cosmetic armor without any progress in converting the old ones are some kind of slap in the face of the people who are still waiting that their beloved armor kit(s) gets converted.
My monk(s) are still waiting for the red leaf outfit with the white cloth wrapped around (leaf 2). I think I have this armor kit on at least 3 different outfits and as soons as there are better outfits dropped ingame I could use this one as a new cosmetic armor. But yeah, if I am the only one who likes that outfit it isn't profitable for you to spend time to convert this armor kit.