HMRC load peaks
While it doesn't affect any of the other aspects of the answers (and being able to transfer the "hardware risk" onto a 3rd party probably does make sense for HMRC), it is worth noting that long term HMRC are looking to flatten the SA filing spike with their MTD proposals - all business taxpayers are being moved to a scenario of quarterly updates in real time (which will in itself increase the average workload) meaning that for a fair proportion of them they'll have all the tax info ready to file for the year within a month of year end, ie by early May.
The 31 Jan deadline will still be there (for those who have other affairs, or multiple trades with non-concurrent accounting dates) but will be less relevant in many cases.
Separately for non-business taxpayers HMRC want everyone to manage things in real time anyway via their Personal Tax Account, and mechanisms like Dynamic Coding for PAYE and Simple Assessments for those with non-PAYE sources of income should reduce the number of full SA returns due on 31 Jan anyway.
Note - although the Income Tax (ITSA) rules aren't mandatory, and won't be before April 2020 at earliest, HMRC are rolling out the underlying tech to VAT returns from April 2019. Unfortunately, what we don't yet know is how many businesses will be able to use the VAT transaction records to drive an income tax submission; but to the extent that they could, it'd facilitate earlier filing for ITSA.
Biting the hand that feeds IT
