First, for a number of practical and legal reasons, "Lumia" has no future other than that determined by the owner of the trademark whether MS or Nokia. MS has ended production of the Lumia line and Nokia seems to be moving forward with Android OS phones.
Spot on. For accuracy, it's Nokia's intellectual property and MS ended production of any mobile phones regardless of what they are called.
If by "Lumia" we are really talking about some Windows OS version cell phone in the future, that might be another discussion, but I would remind you that speculation about a "Surface" phone has been rife for over a year without tangible results.
Make that at least 3 years.