I don't know if Microsoft is among ones practice this approach, but they can potentially discontinue and force users to move on to paid version, once they gain enough user hooked to it.
Though, it seems like Microsoft has been consistent with their Express SKUs for years, maybe this is purely theoretical. (One instance I can think of is TechNet -- but this one, they discontinued it without alternative path, so I guess it's a little different...)
I don't know if Microsoft is among ones practice this approach, but they can potentially discontinue and force users to move on to paid version, once they gain enough user hooked to it.
Though, it seems like Microsoft has been consistent with their Express SKUs for years, maybe this is purely theoretical. (One instance I can think of is TechNet -- but this one, they discontinued it without alternative path, so I guess it's a little different...)