Hi @mdrnd,
I don’t think HubSpot would change something as fundamental as property behavior. (But who knows? You could always suggest it in the HubSpot Ideas section of the community. The product team reviews these suggestions based on popularity.)
However, there is a neat workaround that, I think, accomplishes the same goal for you. It looks like you’re on a Professional subscription which means that you can create conditional sections in the sidebar of your deal record. In other words, you can decide which properties to show in the left sidebar based on the pipeline of the deal that you’re currently viewing. For pipeline 1, you could show properties A, B and C in the sidebar. For pipeline 2, you could show properties D, E and F in the sidebar. By doing this, you could make some properties invisible based on the deal pipeline, avoiding confusion and only showing what matters.
Unfortunately there isn’t a feature like this for mandatory fields during record creation but the sidebar alone would be a huge help here.
Hope this helps!