I don't understand. If the people of kiribati (pronounced KEE-ree-bas) have an S sound, then it makes sense to romanize their language so that words endings with an S sound end with an S letter... If they have a "ti" sound as well, then by all means keep the T and the I, or even glyph them together...

But english is (more or less) a phonetic language. If you're romanizing a foreign language, and it doesn't come out more or less phonetic, then.... try again. It doesn't cost anything to keep an "s" in the prospective alphabet.