The main ethical problem is what would you use as a surrogate mother to bring the clone to term? A secondary problem is we might have difficulty in providing extinct animals with an appropriate microbiome. Another is what about behaviors they would've learned from their parents and/or herd?
Asian elephants are broadly similar enough to be able to bring them to term, assuming we don’t develop an artificial womb.
I broadly support this idea, so long as we implement it reasonably and responsibly. Limit it to a few small islands at first so we can ascertain the negative effects on a limited scale. It should be noted woolly mammoths can swim in the ocean, too, for at least seven kilometers.
Proof:
https://en.wikipedia.org/wiki/Pygmy_mammoth#Evolution
