I suppose it comes down to what is meant by "no hard border" - maybe anything short of a Berlin Wall-style construction could be considered "soft" in the context of a political agreement. Checkpoints and custom posts and airborne patrols are "soft" because the hardened infrastructure is only localised.
Then again, that requirement could be dropped (and the blame laid at the feet of the EU) in order to achieve the version of Brexit that the majority of the Conservative Party seem to be working towards.
Or, the hard border could be between Northern Ireland and the rest of the UK. The DUP won't be happy with that but the removal of parliamentary oversight over any deal has done away with their ability to do anything about it.