Moving this discussion to the Adobe Camera RAW forum.
Lightroom does not use the Camera Raw plug-in. You will have to wait for the next Lightroom update. There is no announced date. You'll just have to wait until it is released.
Or use the DNG Converter 8.7 RC from the same place you got ACR 8.7 RC, then convert your raw files to DNGs and open those in your current LR version.