Thanks for following up on this.
In Austria (and probably numerous other EU countries) regulations are pretty strict on invoice numbering.
In addition to having to adhere to those regulations in many businesses there are existing numbering systems in place – many of which involve having the fiscal year as a prefix and starting from 0001 every year.
While that popular “flavor” of numbering is per se not a legal requirement, it might turn clients away from Snipcart.
My current use case was different though: My client originally opted for generating invoices outside of Snipcart. After a couple of months he changed his mind and now we’re using Snipcart’s invoice generation as intended. It would have been good to start over from 0001 so there is no gap in the numbering (and that IS a legal requirement).
As the invoice generation is already live now, there’s no immediate need from my side – my client decided to do some extra explaining in case of an audit. 
However there are likely scenarios where this could come in handy. So please keep it in the backlog.