For me as for creating poser models on daily basis, there are two things that could be quiet important, preventing having to use P11 for the creations of the models and fully depend on P11 making it even possible to make Poser models. 

1. bringing back the simple material room, or optionally add it as 3rd panel. It simplifies the workflow for basic texturing and is allot faster  when it comes to models with allot of material regions, rather then applying it manually on each just to see how the model looks like . materials can be adapted afterwards if necessary in the Advanced tag. I guess this was the main Idea of Poser having a Simple and a Advanced option instead of a Assign option that is never used !  This feature already makes a creator depend on P11 unless he is new and never knew about the Simple feature in Poser.

2. I do not know if it could be possible, but as we know almost nothing is impossible if there is a will. Making Poser backward compatible with Py 2.7 so that the older essential scripts can be used as there are no replacements for these in P12 and 13 and there will probably never be any as poser seems to have gone through a full reset. Start from scratch. This is for a creator the main reason why he depends on P11  as allot of the scripts developed over decades are essential for a good model creation.

I am not sure if you are aware that also allot of DS creators build up there models in P11 and then encrypt them to DS formats due the better options for rigging and Grouping tools that poser offers. Basically the only platform that DS supports to import fully rigged models ! 

If something New then it should be considered not destroying the options that were build making it possible having all these unique creations that are getting rare due the restrictions caused. Poser as well as DS suffer of a loss of standalone Figure creations the past years that are essential for a good future. Versality is Important not just one Doll witch is the Mother for all further creations just leaving a option of making Derivative creation based on these base models. 

So as Creator somehow just stuck in P11 for rigging and building and may be using P13 just to make the Promo renders or adapting the materials so that they work for the future users of poser.