Allow Arbitrary CI Stage Dependencies (DAG Graphs)

Description

Currently gitlab CI stages have to be specified in a linear fashion:

Instead I'd like to be able to order the stages in an arbitrary directed acyclic graph (DAG):

Proposal

The justification is this would allow fast stages to run quickly, while longer running stages can run in parallel in the background. For the projects / teams I work with this would be a massive productivity boost.

Is something like this possible?