Hi, good question.
To the most part, the same abilities added to the Designer are added to the Report editor in the service. they share alot of the code to ensure (where makes sense) similar experiences.
Depending on the deployment schedule, there is a fair chance you will actually see the features hitting the service before you will see them in the Designer.
Why? there could be technical dependencies that will want us to ensure the capabilities in service before they are made available in the client. the other reason could be simple timing. Designer is being released about once a month where service is every week.
where to expect differences? remember that the service is mostly report editing/authoring where the Designer have full query and modeling environment as such, not all features planned for this summer will be in the service.