RPC allows proprietary software to leverage the functionality of your GPL software, which might go against your intent, as RPC becomes the de facto interface of increasing number of components...
Honestly, I don't buy into the whole non-GPL can't link GPL argument in the first place.
Suppose I were to tell you to grab your copy of the 3rd paperback printing of Game of Thrones and look at the second sentence on page 320. Does posting that sentence make this post a violation of GRRM's copyright? Of course not - I didn't copy anything in his book - simply mentioning that it exists and that it contains a page 320 in no way makes this post a derivative work.
Well, when you link a binary to a shared object, all you do is write a bunch of cross references saying that this function call should be replaced with an address associated with this symbol. Then a linker will replace those references when your code is loaded. None of this involves copying anything. Assuming the shared object is in RAM already being used by something else, your OS isn't even copying the GPL code at all when this happens, but even if a copy were made it is an unmodified copy of the shared object which isn't being redistributed - ie it is permitted by the GPL.
Sure, everybody says that you can't link non-GPL code to GPL code, but I am not convinced that a court is certain to uphold this. I could see issues if you try to bundle GPL and non-GPL software into a single larger work, but if you distribute the non-GPL stuff without the GPL content that problem goes away.
The main issue is no one wants to fight the court battle.
But frankly, this has all been kind of irrelevant anyway - you can distribute source packages, let the client do a compile on install, and ignore the entire affair.