What I can mention right off the bat is that the pictured prototype of the PINE64 PineNote appears to be based on the Bigme B1 (but may change later on). The Bookeen Notéa appears to also be based on the aforementioned tablet, but shares more in common with it than the PineNote does. The pen and case for the PineNote prototype (and the Notéa if I recall correctly) appear to be just the stock Bigme B1 pen and case but without Bigme branding (if originally present).
As such, I feel as though it may be possible to port PineNote system images to the B1 and Notéa following modifications, and vice-versa. I say those images need ot be modified as the median and latter have 32 GB of storage, while the PineNote is purported to have 128 GB of storage, so partitioning will be different. I haven't fully compared the specifications as of this reply, but this could open up the possibility for Android custom ROMs (or even desktop Linux distros with Android subsystems) with the Bigme UX and hardware support grafted on, though with this, I'm currently focused on desktop Linux for the reason that I'm working on a project I'll explain in the next 2 paragraphs.
I've been working on my own open-source Linux-based software platform for e-readers since 2017, currently without a name but with the codename of "Terry", and while I've been busy with lots of research work for that (since I'm designing a new UI based on my own research work and inspiration I found elsewhere), I've been trying to recover from my reaction to the PineNote announcement which left me in tons of metaphorical stitches.
What I can mention is that Project "Terry" is that I attempted to develop it back in around 2017 as Project "Barry", before I spun off the former when I ended up getting so many ideas for features that I had to completely rewrite it from scratch, but also to rewrite it to use a newer Python release and the official Qt on Python implementation. Remnants are on the GitLab public instance, my username there is "kbhasi", but that's old code from before the rewrite I've yet to do, and when I do publish the first bits of rewritten code with the first bits of the new UX, I'll change the "barry-" prefixes on most or of the source repos to "terry-", but the "Project Barry" name will remain for the GitLab group as I'm using that as a temporary name for the organisation that will tie "Terry" and my future e-book projects together. I'm currently doing research and designing the UX based on my research.
(Edit: I forgot to mention that the reason why I'm mentioning Project Terry here is that the specifications of the PineNote prototype appear to be roughly 50-60% close to my predicted system requirements for the former)
I haven't yet registered on the PINE64 forums, but plan to do so.