Multiple cursors sound cool! In vim, you can do something more limited by using visual block mode (C-v) to insert on multiple lines, but you're restricted to insertion on the same column.

The perhaps the closest thing I can think of for your example would be this (starting in normal mode with the cursor at the beginning of your list):

    f_i_Class<Esc>+;.+;.

("Move forward to the next '_', enter insert mode, insert '_Class', leave insert mode, move down one line to the first non-blank character, repeat the forward motion, repeat the insertion, repeat forward motion, repeat insertion." Vim does have word motions, but it includes underscores as parts of words.)

Edit - formatting and a clarification that it's the closest I can think of (I'm doubtful it's the closest you can get).