Из документа Taglist:
*'Tlist_Use_Right_Window'*
Tlist_Use_Right_Window
By default, the vertically split taglist window will appear on the left hand
side. If you prefer to open the window on the right hand side, you can set the
'Tlist_Use_Right_Window' variable to 1:
let Tlist_Use_Right_Window = 1
Ссылка на раздел taglist-options .