But while legacy (ie. non-SegWit) nodes would accept such a transaction, the majority of the network -- and thus the canonical BTC blockchain -- would reject it.
Most importantly (to me), MY NODE will reject it. It won't matter how much hash power they have. They could mine 99% of the blocks, and my node will still reject it because it will STILL be an invalid block with an invalid transaction.
The only people that will be effected will be those foolish enough to still be running a non-segwit enabled wallet on the SegWit network.