... | fzf --preview='bkt --ttl=15m --stale=15s -- your_preview_command {}'

#!/bin/bash
#
# Interactive directory picker using fzf, with a dynamic preview of each
# directory which is cached by bkt. Pass one or more directories as
# arguments and all immediate subdirectories will be displayed by the
# picker. If no arguments are passed your HOME directory is used by
# default.
#
# To use this as a directory switcher define a shell function like so:
#
# goto() {
#   local dir
#   dir=$(/path/to/dir-picker.sh ~/Workspaces) || return
#   cd "$dir"
# }

# Use a dynamic scope for bkt so we don't surface stale results or collide with other usages
printf -v BKT_SCOPE 'dir-picker-%(%s)T-%s' -1 "$$"
export BKT_SCOPE

# Renders the preview window displayed by fzf
# Currently it simply shows the directory contents or git status
# for git repos but could be expanded to do more complex/slow work.
# You could move this out to a separate script instead if preferred.
preview() {
  cd "${1:?}" || return
  printf '\e[93m%s\e[0m\n\n' "$PWD"
  if [[ -e .git ]]; then
    git -c color.ui=always status
  else
    ls --color=always -oh
  fi
}
# Export the preview function so it can be called by fzf's preview subprocess
export -f preview

# Command to execute the preview function via bkt, so that repeated invocations
# are cached. The directory needs to be specified as an additional argument.
PREVIEW_CMD=(bkt --ttl=15m --stale=15s -- bash -c 'preview "$1"' -)

# Caller-provided set of directories to search
DIRS=("$@")
if (( ${#DIRS[@]} == 0 )); then
  DIRS=("$HOME")
fi

# Enumerate all subdirectories, these will be passed to fzf
readarray -t CHOICES < <(find "${DIRS[@]}" -mindepth 1 -maxdepth 1 -type d)

# But first kick off a background thread invoking bkt on each directory.
# This isn't necessary, but helps warm the cache so fzf is more responsive when it starts.
#
# This could be implemented using bkt's --warm flag, but instead we intentionally
# process each directory in sequence to avoid running potentially dozens of expensive
# preview processes concurrently and needlessly. A user who scrolls up quickly may
# have to wait, but the first few directories should be warm by the time the user
# starts browsing.
(
  for d in "${CHOICES[@]:1}"; do
    "${PREVIEW_CMD[@]}" "$d"
  done &
) &>/dev/null

# Launch fzf! The PREVIEW_CMD is escaped with @Q before being passed to fzf so
# that the command is properly quoted.
printf '%s\n' "${CHOICES[@]}" | fzf --select-1 --exit-0 --preview="${PREVIEW_CMD[*]@Q} {}"