Right now psycopg2 is required to be exactly version 2.6.2, which makes it mostly impossible to install pgadmin4 without having the postgresql C development packages installed (since you need to rebuild psycopg2 from source to make that work, given that few platforms ship *exactly* that version).
I suggest just saying "2.6 or greater", which should make it work on many more platforms.
AFAIK there aren't any other packages with similar compile requirements, so the rest seem OK.
