They've been talking about this for years and years. I can't see how it will work without people getting caught in the crossfire who shouldn't be. They say they're looking for people receiving more than £1000 a year, but that could easily be someone selling their personal possessions.
It's possible that someone could have a turnover of £1000+ in a year from selling personal possessions, but that wouldn't mean there would be a tax liability. In the vast majority of those cases the possessions would be sold at a loss, simply because second hand goods are cheaper than new. So if HMRC did insist on them making a tax return there would be no tax to pay anyway.
And if HMRC did view such activities as a "business", the income and expenditure would be cumulative for the whole year: ie, if you sell ten items and for some reason one of them makes a profit, it would still be offset by the losses made on all the others.
So the very worst that being "caught in the crossfire" would mean is an increase in bureaucracy. In practice however, I very much doubt HMRC would use this to get people registered as businesses who really aren't. HMRC hate unhelpful bureaucracy as much as anyone, particularly when it costs them in man hours and overhead to process without actually bringing in any more tax receipts. There's no reason they would want to get a whole load more people submitting SE tax returns and then paying nothing.