Just wanted to share that iPGMail on iOS as of today supports EdDSA keys.
I had asked the dev to implent it since I use an EdDSA GPG key.
You may have read or heard of EcDSA, I find it confusing so here is a simple explanation of the differences https://www.reddit.com/r/crypto/comments/7js477/comment/dr8xdak
That is awesome. Overview of current (save) curves here https://safecurves.cr.yp.to
So if you have a modern GPG key you are now able to use it on iOS too.