The big issue I see with this is that the new rules do not mandate any kind of identification on packages that have the VAT already paid, so they can't identify VAT-unpaid packages.
And as the seller is now responsible for VAT for B2C consignments under £135, I'm unsure if they can extract the 20% from the recipient anyway.
I'm guessing that at least for now this means everything valued under £135 is going to go straight through, and they'll implement something sane later...
Something similar happened to me. On top of the £8 charge, I had to drive 30 miles to the depot to pay the charge. The Royal Mail refused to deliver it.
So they are well prepared to confiscate your package sent to the UK until you pay up.
(And your courier/Royal Mail will charge you another £8 for the hassle just to rub it in.)