Re: Draft statutory instruments
The reason why draft statutory instruments are required is because there is no hope whatsoever that all of these amendments could be debated by both houses in this century, let alone before March 29th. They need to be draft now so that they can be waved into effect with a single vote on March 29th if a deal does not get agreed. We don't (and in fact can't) bring them into force now, because the EU bills are still in effect.
The main purpose of the process is that each EU article enacted into UK law needs individual scrutiny to change the wording to remove references to the European courts and the other legal entities in the EU, and replace them in the legislation with the appropriate UK bodies. This is what prevents the wholesale bulk change of the relevant laws.
Whilst there is the possibility that other changes could be made during this process, that was not the stated intent of the legislation that was passed to allow this all to be done as SIs.
Like many other Brexit related processes, we as non civil servants don't actually find out about the things that need to be done unless we look. The whole process is hugely complex, and there will still be things to be done long after March 29th. We really needed the whole of the two year period (and potentially more) to put in place the mechanisms, whatever the outcome (and the deal has this built in to the transition period), but not enough has been done for a WTO exit.
The thinking was that a no-deal exit was unthinkable, so didn't need to be planned for. Unfortunately, the people who thought this were over optimistic...
(Much as I don't want it, I can still see Article 50 being rescinded on March 28th, because the enormity of the mess if a deal is not found is only beginning to sink in to politicians heads!)