We should all work on the assumption that HMRC can receive data from eBay (and other platforms) going back years if requested by HMRC. Same for HMRC and your bank. So if you know you are not currently compliant then don't assume you have another year to put things right - do it now. However, if you are following the rules then nothing changes - private sellers can sell their own items (i.e. not selling for profit) without needing to do a tax return or pay tax. That hasn't changed.
I expect that the new legislation is not targeting individuals whose sales total a few thousand pounds a year of used items, but larger scale operations that could mean tax evasion, VAT fraud, money laundering, counterfeit goods etc. Broadly we should all support efforts to track down any such offenders - taxes illegally not paid is lost public spending (on schools, hospitals, roads or whatever you like to think our taxes are best spent on).
