Hey Grum, I’m one of the devs who’s working on the new animation stuff.
Thanks for all of the great feedback. 
(1) Speed spin editor height is very small…
Yeah this is a bug/regression introduced a few days ago when someone changed the button styling. It’ll be fixed!
(2) Oignon and menu are far-far away than other buttons…
Well, the basic idea is to present the most commonly used workflow items (the buttons that we press most often as animators) right out front while moving the set-and-forget configuration widgets into sub-menus. We could have aligned the sub-menus to the left, but I think it’s more of a clear design to put actions on the left and sub-menus on the right. Eventually we will be moving other sub-menus, like audio, over there as well so I think the design will become more clear over time.
Please give it some time to grow on you, and if it still bothers people a few versions in we can always change it.
(3) In krita 4.x there’s more navigation buttons
Yeah, that’s true. We’ve opted to remove the first keyframe and last keyframe buttons because we now have a stop button that brings us back to the first frame and there really isn’t enough practical utility in jumping to the last frame to justify the extra button. (Jumping to the last frame is still possible via hotkey actions, though.)
I’m still thinking about what we should do in regards to the previous/next keyframe buttons. It’s definitely useful, but the main issue is that we have a lot of different actions for jumping to keyframes now (like jumping to the next keyframe of the same label color, and I think jumping to the next visible onion skin key is in our todo list), so the questions are (a) which of these needs a dedicated toolbar button and (b) is there a way to support these things without cluttering the interface too much and making it harder for new users to understand.
We will work on it, but for now please bind a hotkey to the previous/next keyframe actions.
(4) Auto frame mode
Hmm, I’m not sure. Is the auto frame mode something that you change often while animating?
In my experience, I usually just set it once and then draw a whole bunch of frames, but I know that everybody has a different workflow.
(5) Speed control in settings menu
This was the case a few months back, but we were asked to move it out onto the toolbar! 
I personally don’t interact with it too often while animating, but some people like to use it to preview their animation at different speeds without manually scrubbing, so we went with it.
It’ll stay on the toolbar for now until we really start running out of space.
Anyway, @eoinoneill and I will take all of this feedback into consideration. I really want to make a big impact when it comes to improving animation workflow in Krita 5, so I appreciate your input.
Thanks!