I've sort of tried something similar, a long time ago, in Lightwave. Lightwave isn't Poser though, but the version of Lightwave I did this in did not have many of the advancements Poser has now that are almost taken for granted in Poser (it was V5.6 of Lightwave, where despite group names, bones could affect nearby meshes). It worked well enough for what I needed at the time.
I believe, though I am not certain, that I have a few legacy items for the Generation 3 figures that did something just like this. I need to double check, but I am going to say it was either something from Uzilite or Aery Soul (or what name he was using then).
Morphs could be built in to smart propped buttons, but that is a lot of extra work - and then limits them to the morphs baked in. I do have some experience turning props into morphing smartprops using morphs and geo-switching. It's been a minute since I did any of that (before RDNA closed)...but at the time I was working with several independent vendors on morphing props, geometry switching props and figures, and ERC...lots of ERC.
Edit Oh, yeah, Uzilite's MOS line uses a lot of child groups and embedded Smartprops which has caused me no end of trouble trying to convert them from V3/M3 to other figures. The Shoulders on the MOS MArine have fold out tools that break using both Crossdresser and Wardrobe Wizard, The helmet from Liquid Knight has many children that break on conversion. The belt items on either of these sets use embedded props that get lost with the conversions - but on the figure they are meant for they work great with poses.