That's how it used to be prior to 2015, i.e., only 2 weeks between RG and Wimby. The 3rd week was introduced only since 2015.The point is not Halle or Queens, the point is one week less between RG and Wimbledon. The time to switch from clay to grass is very short anyway, and one week less makes it even worse. But let's see what Federer decides, in case RG really happens with one week delay.
I think Fed will play RG, regardless. Semi is the max. he will get to at RG, so his run will end on Friday at RG, that too if he gets to the Semi at RG. Then he will have his first match at Halle the next Wednesday. That's enough time for him to recuperate for the grass.