Remote Desktop Protocol 10, which is already available on Windows 10 Technical Preview, has a new feature called Zoom Option that would be a solution just for that.:

Remote Desktop Protocol 10, which is already available on Windows 10 Technical Preview, has a new feature called Zoom Option that would be a solution just for that.

To be able to use Zoom Option feature, you will need to run RDP session in a sizeable window (not in Full screen mode). Right-click the top board of the RDP window, and choose Zoom Option, then pick a scale number to zoom into, from 100% all the way up to 300$.

Next ..

As you can see, because the zoom option is not done on the host computer, the result isn’t clear and crisp. But it does help and would be a nice work around when connecting to an old system from a HiDPI computer.