There are at this point only two (or at least two, depending on how you look at it) show-stoppers for retiring my 2010 addons.
1. Ground views of launchpads. They have deep dugouts - and in 2016, anything "below 0 mark" is filled with ground texture. Recent flattening feature improved look and feel greatly, but dugouts are still outstanding - totally ruins visual impression. Taking off may be only 1% of the mission time - but it is the percent that most people are most familiar with from launch reports.
2. 2010 touchdown points behave really unpredictably. My collection now has over hundred(!) of individual vessels with config files with defined Orbiter 2010 TDPs. About 50% of them work the same in 2016. About half of the remaining vessels work "so-so" and the "other half" - don't work at all, no matter what I try. I have an item in my plan to add 2016-style touchdown points - but then I'll have to go back and set and test those for all 100 vessels! Quite a task to just reinstate something that already used to work... chances are I won't get to it until I figure out some way to script it.
These two are the biggest. There are a couple more smaller things - for which I know solutions, but which still have to be actually solved
. Like this Vostok/Vzor issue, or ground textures conversions (which are done for my areas to about 80% of my liking, with remaining 20%, unfortunately, following the universal 80/20 effort rule).
And another purely personal obstacle - it happens so that I currently have to do my development on a non-gaming machine. For 2016, every Orbiter launch takes sometimes almost a minute to load all ground textures. If you are, for example, tweaking some geometry or placement or those touchdown points - you have to launch scenario so often it becomes impractical. You start tinkering with your environment to try to speed it up instead of thinking of what you are working on. So things are much easier done in 2010 first, then, when all is done, tested in 2016 (and, when it gets really intense, on a better machine).