Are you sure about the Canon RF 100-400mm f/5.6-7.1 IS USM, could this be for the M and not the RF?
https://www.canonnews.com/canon-patent-application-canon-rf-100-400-f55-71
Beware - Eligibility: Open to legal residents of Digital Products - Worldwide | Physical Products - USA who are 18 years or older.
UK are not eligible for the Physical Products
This is already out there, does the same thing and only takes a second or two to take multiple shots.
http://www.heliconsoft.com/heliconsoft-products/helicon-fb-tube/
I use it and it's perfect, comes with the Helicon software as well.