Here you go: The new GoPro firmware update (v5.0) is compatible with your SOLO app video feed and settings will work just fine, however, it will no longer turn on along with your SOLO unit. This is permanent and probably that functionality will not be re-enabled for the new GoPro Fw, although this is not a final decision. Besides that, there's a video codec change that alters the video feed when recording on 2.7K and 4K. It will simply zoom the image that is displayed in the app (the live feed), but the video recorded on the GoPro itself is not affected by this.
In case you want to revert firmware to v3.0 to regain old functionality, the steps to downgrade the GoPro Firmware below:
1. Download the UPDATE.zip file for your camera. GoPro Firmware
2. Extract the files with the option Extract to UPDATE
3. Insert the SD card from the GoPro into the computer
4. Copy the UPDATE folder to the microSD card
5. Insert the SD card back into the Gopro
6. Turn on the GoPro. This will perform the downgrade (the camera will restart itself about 4 times during the downgrade, this is normal).