Surely, if PwC is wrong, and Patreon is responsible (which seems this way) and HMRC decides to investigate, they will go after Patreon, and not individual users?
Correct, although I'd be very surprised if this actually happened. HMRC has enough trouble staying on top of non-compliance and lost taxes in the UK, let alone chasing people for VAT due in other EU states. I can't imagine HMRC being too quick to rush to become a debt collector for other EU states.
Bear in mind that if people merely keep operating now as they did in 2014, HMRC loses nothing - it's only the tax authorities in other EU states who lose out. While no-one should take this as legal advice, I suspect all we'll see is other EU tax authorities taking action against the biggest non-compliers rather than individuals.