They are likely going to be available for a while. As was posted in the original post, if they (STS) see that they are a success, then it will be permanent. This is more or less an experiment. From what i can see, there are 2 profitable reasons for them to keep this:

Reason one is people will buy the kits to sell them. This means more elixir purchases for that great plat to gold conversion of 1:3,000.

Reason two is that the regular plat-buyers will still buy elixirs for 4 plat to use them. If they buy them for gold, then they lost profit potential. 1 plat is worth 1,000 gold. 9-13,000 (price of a kit) gold = 9-13 plat. It's a better deal for them to buy with plat.