The RPi does not do every video with hardware decoding. HEVCon the RPi is done via software decoding using various tricks.
Klojum - ok ... so does the Rick Pi 4 then ?
Deinterlacing happens automatically, the settings that are greyed out are for software decoding, not hardware decoding that is used on all RK3399 devices.
Yes Rock Pi 4 supports H264, H265 and VP9 hardware accelerated video playback.
The bookmarks problem is a Kodi problem that will most likely be fixed by Kodi Team.
Deinterlace is configurable under Open-GL (on x86 hardware) but not when using Open-GLES (on ARM chips). They are distinct and quite different ways to render video on-screen.
If things take 50 seconds to boot there's an issue somewhere. Sharing the systemd journal log after boot should show where the delay is; unless the issue is in u-boot before the kernel/system (which generate the boot log) run.
Please understand that RK development is "work in progress" and far from complete. Playback glitches should be expected.
Kodi GBM/V4L2 support is still in a fluid state as the underlying changes to Linux kernel things aren't cast in stone yet, but at some point they will become a more static target, and from that point forwards change becomes much easier to manage. Support on the Kodi side really comes down to GBM/V4L2 providing a single code-path into FFmpeg which handles a small number of different code-paths (stateless, statefull, vaapi) depending on which SOC or GPU hardware is being used. There are 5-6 developers actively working on that area of code; roughly representing RK, Allwinner (stateless) and Amlogic, Raspberry Pi (statefull) and Intel/AMD (vaapi) interfaces. Once you drop lower in the stack to the kernel driver code things appear to be more of a one-man effort because kernel DRM drivers tend to have a primary maintainer driving things forwards, but in all cases there's a community of other developers actively testing and contributing towards that driver and the surrounding stack. LE tends to have a single developer 'representative' among a group of developers working on code and influencing direction. We actively and successfully position Kodi as a fun and useful test application, and since many of the community developers have competing professional or commercial interests we often fulfil a role as a neutral test-case and it's common to see "good Kodi support" somewhere on the written agenda for V4L2 graphics initiatives.
Rockchip (and others) are in limbo at the moment while we wait for some upstream kernel changes to land. This is completely out of our control but it will happen (as big companies like Intel need it to) and then we'll start to show progress again. Raspberry Pi and its legion of supporters are ultimately dependent on the same changes and will also be moving wholesale to the Kodi GBM/V4L2 stack for LE10. Many things become interconnected in a way that makes it impossible to promise that Rockchip support will not drop off, but equally these changes makes it fundamentally more improbable this this will occur 
If it's in the Kodi repo it's device agnostic and should just work. If it doesn't, flag the issue to the add-on author via Kodi forums.
