my macro script will fake poly cage method in modo. basically you will have half polygon model half subd model in the same view (mirrored). you will be able to do vertex and edge operations, deform operations etc. only draw back is that you cannot select any polygons and work with polygons. this is a cheat method not an implemented feature by luxology as far as i know. it works because due to the way symmetry handles objects in modo, i think based on coordinates of vertices. that is why you cannot work in poly mode. but you can use element tool or drag tools etc on polygons without hesistation as far as i know. just do not select any polygon and aply operations and assume that it will appear on other side. actually you can work on polygons, just you need to select both sides manually if you want to apply lets say bevel, in theory bevel will create equal vertices in each side
it wont be like other softwares implemented features like mayas. but it is pretty good start, and can be cool to use it at least once in a while to check out your model in shaded cage model. well if you do not like it you can just enable wireframe cage anytime anyways
make sure that you have half of the model ready to go, and you have just one half and it should be in subd, if not otherside will appear as subd. great thing about this is that, you can just press tab and otherside will become opposite 
i came up with tthe idea because there were alot of people on the board wanted such feature, i am hoping this one came close
and this works base on symmetry x
if you want other axis, manipulate the macro, or record one for yourself
#LXMacro#
select.symmetryAxis “off”
select.invert
tool.set “actr.pivot” “on”
tool.set “poly.mirror” “on”
tool.setAttr “center.pivot” “cenX” [0 m]
tool.setAttr “center.pivot” “cenY” [0 m]
tool.setAttr “center.pivot” “cenZ” [0 m]
tool.doApply
select.nextMode
select.invert
poly.convert “face” “subpatch” [1]
select.symmetryAxis “x”