I actually think it is ok to cross Cemani for your own use and enjoyment. The problem is that people are selling the crosses as "Pure Cemani potential" or even worse, they are calling them Kedu. Ayam Kedu are the clear skin version of the Ayam Cemani. Basically they are a different color preferred by the Dutch when they were in Indonesia. They are not crosses. The part that irritated me is that people selling the crosses copied directly from an email message I said to them and did so incorrectly. Basically if you breed hundreds of Kedu, you many randomly hatch a Cemani. This is how Ayam Cemani were created. Over years of hatching local indigenous breeds, a random mutation of all black appeared. They took that to mean that you could cross Cemani and produce Cemani from the crosses. If you don't have the FM genes, you can't cull to create it. Their "Pure Cemani potential" had 100% pink feet and white toenails. They looked more like black australorps than Cemani. They will never be Cemani.
So I don't have a problem if people want to create their own mixes. Just please do the Cemani breed a favor and leave out any mention of "Cemani" in the name. The poor breed has enough scammers trying to take advantage of people that don't do their own research before bidding on eBay.