ARC 8.5 has a new filter brush for the graduated filter which will allow deleting areas from the applied area - why/how can ACR 8.5 be set as a external editor to allow access to this ability??? . Or when will Lightroom be upgraded to have this feature?
ACR 8.5 is a plug-in for Photoshop not a standalone program. I’d suggest doing an Edit In Photoshop CC/2014 and then using Filter / Camera Raw in PS to do your edits.
I would also LR will be upgraded at some point, but maybe not until 6.0. It’s hard to say, since the LR folks are having to deal with LR mobile things, now, too, PS is part of the cloud, and a promise of the cloud is to get new functionality sooner.