Looks like they plan to have the blue line extension ready to go in 2029 mentioned in the embedded video not the article.
The plan is to have 55% of the population within 800 meters of public transportation stations by 2040.
A little bit old, but I always like to watch the video linked below: Youtube - Dubai Progress by MetroCucumber
Dubai expands in both directions. It actually has a short coast line that warranted building additional coast. There will be more lines in the future too.