I'm probably in the minority by far with this, but I think MK might need new e-tickets foremost. This is because MK is representative of WDW to most guests, and so it needs to be the best first/main impression of WDW in order to stay ahead of Uni. Many people view MK as "Disney" and will compare it alone against Uni. And that could be a major factor in word of mouth about spending more time at WDW vs Uni, staying at WDW vs Uni, etc. (Of course, Disney should also keep trying to do a better job getting across that WDW is four parks, etc.)
New MK e-tickets might not increase crowding anyway, because most central Florida theme park visitors go there already. Plus, it can be in conjunction with added acerage via land expansions.