Any drawbacks in sharing service class's member variables across components in Angular2?

This is a valid way to share properties. Services in Angular are simply singletons within their given provider scope. However, I would say that this is does not closely match a canonical way to share properties for two main reasons:

1. The component values can be changed without the changes being reflected in the service
2. Change detection will not be processed if the value reference within the service changes
   • As a side note on this, change detection will also not be processed on object mutation if the more efficient ChangeDetectionStrategy.OnPush strategy is used

Using Observable objects in the service could help mitigate both of these issues. For example, using BehaviorSubject objects would allow components to change the value provided by the service (via BehaviorSubject.prototype.next(value)) and to subscribe to the service-proivded value to efficiently perform change detection (done simply through the async pipe when in a template). BehaviorSubject objects also conveniently have the getValue() function to synchronously get the existing property value if needed.

That being said, using Observable fields does have an additional cost and its benefit depends on your situation. I suggest sticking with the KISS principle and keep what you have until you'd actually benefit from doing anything more complex.