The first of the two firmware updates promised by Panasonic for its new GH5 this year will be released on April 24, with v1.1 firmware adding 4:2:2 10-bit Full HD video capture to the existing 4K video mode.
There is not really much to report above and beyond that to be honest. As DPReview writes, the firmware brings 4:2:2 10-bit IPB capture at 100Mbps to 1080/59.97p resolution to the $2000 camera. Anamorphic shooters also get 10-bit 4:2:2 IPB capture but with the larger, 3328 x 2496 shooting region encoded at 150Mbps.
A couple of bug fixes have made it into this update too. A problem in which the exposure adjustment did not operate properly during live view standby under specific conditions using [Variable Frame Rate] has been fixed, as has another where afterimages appeared when recording video under high ISO sensitivity settings using [V-LogL].
That means users will have to wait until at least the next firmware update, due in the summer, for a fix to the rather more serious autofocus issue that has been lighting up various GH5-oriented parts of the web in recent weeks. The only statement made to date by the company on all that was released, somewhat bizarrely, in a video uploaded by Lumix Luminary PhotoJoseph, with the key takeaway being the sentence "Panasonic pledges to further improve the AF quality."
Other features to come, according to DPReview, include the possibility of higher resolution anamorphic video capture, along with 400Mbps All-I capture for 4K and 200Mbps All-I capture for Full HD video.