What do you think would be the key factors to drive mass adoption of D?

[Dejan Lekic]

It is very simple - you will not see mass adoption if average 
user needs to spend days, weeks even months implementing "missing 
pieces" for her/his project.

D lacks fully tested and fully-featured packages that are 
comparable in quality to packages for other languages. D 
ecosystem has thousands of packages (projects) that do something, 
but that something is in 98% of cases a very limited feature-set. 
Kudos to those who went "extra mile" and implemented fully 
featured packages.

I already hear people saying "those who want those missing 
features are welcome to submit PRs". - Sure, but why would they 
even decide to use D when they know they will spend days 
fixing/improving incomplete D package(s), when they simply can 
turn to Python, Go, Rust and find everything they need to get the 
job done?