As you noted, Allow users to select a dashboard on their lightning home page is an idea asking for this functionality.
What you do have is:
- Ability to create different lightning home pages for different profiles. See Build a Custom Home Page for Lightning Experience trailhead.
- Within that home page, you could drag multiple dashboards on the page with specific conditions to display only for certain users. This design won't help if you need 50+ differences for 50+ users, but it will help if you have specific groups of users that need different dashboards (ex. Sales Leads view vs. Open Opportunities vs. Manager dashboard).
- You could look on appexchange, there's Dashboard Pal which seems like it might provide what you're looking for (I have not used this so I cannot say for sure if it's good or meets the need). See description of it below
The lightning component enables the user to choose a dashboard from a
list of available folders in the org, upon selecting a dashboard this
dashboard is saved for current user, replacing the default dashboard
for that user in order to avoid having that user having to select a
dashboard every time, therefore making the user interaction
persistent.