there is now a little tool, that can be used to contact someone if you have the PGP key and their E-Mail-Address:
note, that this tool is for nerds only and is not officially supported by Delta Chat or is recommended in any way.
in the vast majority of cases, it is better to use chatmail and to scan an QR code or to send an invite link. still, if one wants to, it is posssible to contact classic PGP this way now 
add the tool eg. at “Saved Messages / Attach / App / .asc to VCard”
source code is at https://codeberg.org/r10s/asc-to-vcard