The details of the new digital accounts which tax payers will have and how their sources of income will get on to the accounts is very sketchy at present. The idea is that taxpayers' details of pension income, employment income and interest income will be entered automatically on to these digital accounts via employers RTI returns and banks. That part is relatively simple though there's a risk of errors.
Self employed people would need to use accounting software to record all their transactions and that software would automatically get transferred to the digital accounts. I can see major problems and errors arising there.
Then there's the other sources of taxable income such as rental income, dividend income (higher rate taxpayers have to pay the higher rate tax on that), capital gains and other things. People will have to be able to inform HMRC of these some how.
The intention is that people will be able to see what their tax position is throughout the year right up to date and can pay tax during the course of the year rather than January and July on the present self assessment tax return system.
More information as to how this will be done is supposed to be published later this year. To be implemented over the next 5 years, I can see it taking longer than that with the technical problems that will have to be dealt with.