I just started using Skiff a couple months ago. I enjoyed the quick alias features and the multiple aliases to keep everything separated. I am really sad to see this happen so soon after joining.
You can work around the need to go around updating all sites with your new email address... at least the next time you need to change your email address.
I use SimpleLogin to create a unique alias (on my own domain) for each website. When I finally migrated to Proton all I had to do was add the proton email address to SimpleLogin and delete my old GMail address to get it to point to Proton (I started migrating to aliases before moving away from GMail). Likewise if I ever move in the future I only need to update SimpleLogin. I was looking to move to Skiff when my Proton renewal was due!
To set this up I had to obviously update every single website which was very time consuming. However I have much better protection now as email addresses are disposable should a site start spamming me. The only site that actually knows my Proton email address is Bitwarden, Proton itself and SimpleLogin.
Looking in my account I have over 300 aliases. Crazy.