I'm not sure why this is news, since PlexBMC has been an available plug-in for Kodi for at least the past several years.
I suppose it's just a matter of that the Plex plugin for Kodi was essentially a DLNA client, which the usual crummy presentation that goes along with that, but IIRC it did show friends' Shared Libraries.
I use Kodi at home for personal media access, but I have a Plex Server that shares the same content for external access as well. I hardly ever use it, but I certainly can. The libraries between the two are already lined up, though Kodi and Plex each have their own database and metadata storage. If the two can reconcile those two things so that I only need one back-end for both, that's something I care about.
(Why Kodi/SPMC over Plex? Kodi offers better support for high resolution audio and has support for third-party tools for video playback, just in case I feel like throwing a GTX1080 at 4k upscaling or something).
If, on the other hand, this is just about getting a more polished interface for Plex libraries in Kodi than the one I had via the old Plex plugin, all I can say is "meh."
I'm a lifetime Plex Pass member, but they haven't done anything in years that makes me think a Plex Pass is anything but a donation to the project. I don't care about Kodi integration. I'd rather they work on getting music libraries to suck less or improve content filtering than get cloud streaming or Kodi integration or whatever other bullshit they've been doing lately.