Ethyopian Jews should use an Hallachically valid Hagadah if they are Orthodox, or follow their own rites if they are not. And a Kahane Hagadah seems also odd. What's the difference with the traditional versions? If it has references to present day Israel, I doubt it is Hallachically valid, since there are no sages who can validate a Nusach today.
What are you talking about? Everyone makes their own hagadah. It's about the perush, not the nusah.
In any case, the nusah was made in the time of the gaonim, so who says we can't edit things or add minor things, or alter in any way with word changes, etc? Look at the Rambam's hagada in hilchoth pesah and you will see it is not exactly the nusah in your favorite family hagada (although almost the same) that we use today. That is because there is no reason one should not be able to touch it up and people did do so. But in any case you have hundreds of hagadas of different people all giving their own rendition on different aspects of the same basic nusah.
Furthermore, my gemara rebbe argues for a girsa correction in a few places and does a few different things in his seder. The ikkar is not the nusah of the "baal hagada," (whoever amongst the gaonim who authored the 'official' text that we use), the ikkar is the halachic requirements for the pesah seder night as explained in the Talmud. In other words, a few basic requirements (which are included in the popular nusah but with tons of extra material added) plus the associated mitzvot including kiddush, the four cups of wine, etc etc. But the text of the hagada itself is not specified in the gemara... and in fact a mahloketh exists between rav and shmuel over what to say and we include both their opinions... plus a whole assortment of extra things.
In any case, although I don't know, I find it likely that the "Kahane hagadah" is merely a new peyrush on the same nusah like so many authorities have done throughout history - ie the malbim hagadah, the vilna gaon hagadah, the maharal hagadah, the rav soloveitchik hagadah, etc etc you can see a million of these in sefarim stores.
In any case, Raul, I understand that you are not Jewish (according to what you told us), so my intention is not to teach you Torah, but when you make authoritative statements in the name of Judaism here, expect to be corrected. Not that what I did here falls into the category of "teaching you Torah" anyway, but just so we're clear.