Segwit has the issue of being totally reversible. For the coins or transactions done on Segwit they can be manipulated successfully by a 51% attack so well that they won't even have transaction IDs on the Segwit chain any more.

If you choose to use Segwit you are risking a 51% attack miner who can literally take the entire history of the blockchain of Segwit, wipe it, and take the coins.

As it stands now with the current BTC blockchain it is unlikely that a 51% attack can affect more than the last 2 or 3 blocks.