Wherein I do really bad things to hash constructors again.

path_explode_hash.rb

path_explode_hash = Hash.new { |hash, path|
  if path == :*
    -> {
      prev_paths = [:*]

      recurse = -> next_path {
        if next_path == :*
          prev_paths.push(:*)
          recurse
        else
          [*prev_paths, next_path].reduce(hash) { |target, path|
            if path == :*
              target.is_a?(Array) ? target.flat_map(&:values) : target.values
            else
              if target.is_a?(Array)
                target.reduce([]) { |a,t| t[path] == {} ? a : a.push(t[path]) }
              else
                target[path]
              end
            end
          }
        end
      }
    }.call
  else
    hash[path] = Hash.new(&hash.default_proc)
  end
}

path_explode_hash[:a][:b][:c] = 5
path_explode_hash[:a][:b][:d] = 6
path_explode_hash[:a][:g][:d] = 7
path_explode_hash[:a][:g][:c] = 8
path_explode_hash[:a][:m][:d] = 9
path_explode_hash[:a][:m][:x] = 10

p path_explode_hash[:*][:*][:d] # => [6, 7, 9]
p path_explode_hash[:*][:*][:x] # => [10]
p path_explode_hash[:a][:*][:x] # => [10]