notes:

• this was developed on macos (and qwertz keyboard, in case of shortcuts like alt-c/alt-p which is also ç/π on my keyboard)
• only requires fzf and jj (pbcopy won't work on other systems though, replace with another copy to clipboard cli or just remove the copy commands)
• it's important that the commit id and change id consistently stay in the same position, I've had to modify builtin_change_id_with_hidden_and_divergent_info to achieve this. Play around with the columns in the config until the correct one is extracted
• the node symbols you use have to be configured, this is necessary to detect "real" lines when using multiline log
• do not use any of the commands in the obslog view, I have yet to add :transform to all of them to prevent them from working in that mode

The base of primitives here is excellent. Thanks so much!

I took most of the primitives here, kept my original idea of eval()-ing the query, and made the bindings more vimmish (i learned you could do this using change:clear-query + binding to single keys). The result is a huge QoL improvement for me, because I get to keep all of the Emacs-style keybindings to edit the query + I like single key bindings anyway.

#... config and variables
becomeNormal="change-prompt(NORMAL MODE: )+rebind(change,i,j,k,n,E,A,d,U,O,y,Y,space)+unbind(enter)"
becomeInsert="change-prompt(INSERT MODE: )+unbind(change,i,j,k,n,E,A,d,U,O,y,Y,space)+rebind(enter)"

eval $baseLogCommand |
    fzf --ansi --exact --reverse --no-sort --no-info --phony --prompt "NORMAL MODE: " \
        --delimiter "$delimiterPattern" \
        --header 'Press ? for help, ctrl+q to quit' \
        --preview "$command --ignore-working-copy show --color-words {$commitIdColumn}" \
        --height 100% --preview-window right \
        --bind "change:clear-query" \
        --bind "j:down" \
        --bind "k:up" \
        --bind "n:execute-silent($command new {+$commitIdColumn})+$reloadLog" \
        --bind "E:execute-silent($command edit {+$commitIdColumn})+$reloadLog" \
        --bind "A:execute-silent($command abandon {+$commitIdColumn})+$reloadLog" \
        --bind "d:execute-silent($command describe {+$commitIdColumn})+$reloadLog" \
        --bind "U:execute-silent($command undo)+$reloadLog" \
        --bind "space:execute($command show --ignore-working-copy {$commitIdColumn} | $pipeToPager)" \
        --bind "O:change-prompt(OBSLOG MODE)+$loadObsLog+first" \
        --bind "y:execute-silent(echo -n {$changeIdColumn} | $copyStdinToClipboard)" \
        --bind "Y:execute-silent(echo -n {$commitIdColumn} | $copyStdinToClipboard)" \
        --bind "enter:execute(eval {q})+$becomeNormal+$reload" \
        --bind "esc:$becomeNormal+$reload" \
        --bind "i:$becomeInsert" \
        --bind "start:$becomeNormal"

I'll probably post something somewhere sometime.

Updated this one to be more vimlike as well, you can enter revset mode by pressing i, entering a revset and submitting it with enter, the revset is then persisted in the FZF_BORDER_LABEL and can be cleared again by pressing enter with an empty query in revset mode.
obslog is also a separate mode with only a subset of keybinds supported.
I'm thinking about also adding a command mode for your eval needs