I really like the idea of circuits.io. Here some things i noticed during a short test. (Probably you already know all these things)
Some kind of an "Push Obstacle" Layout mode would be nice. (Move the obstacles when you try to lay down an wire) Or at least a "Walk around Obstacle".
Have an adjustable keymapping. (i prefere to have zoom on "A" + "D", pan on "W", start routing on "S" etc. )
I wasn't able to change the layer (| is Alt+7 for me which your app doesn't seem to recognize)
Add more layer and Polygons/Planes. (Our standart pcb has 4 Layers. GND, VCC, 2 times routing)
The device search is just lame.
It would be nice to be able to edit a project as a team. (Have a history of changes and who made this changes, add a possible to review the changes, etc.)