I spoke to Steinberg support this morning. The support guy was helpful, but did not have any new information. He did clarify that since the plugins are listed on the compatibility page (https://www.steinberg.net/nc/en/support/knowledgebase_new/show_details/kb_show/steinberg-product-compatibility-info-regarding-mac-os-x-1010-yosemite.html), then there is an intention to fix the issues eventually.
He did promise to check with the developers to see if there was any new information and especially to ask if they anticipate any problems.
He also confirmed that they have prioritised their development effort towards the more mainstream products, which is understandable, given the scale of the difficulties they have faced with Yosemite compatibility.
I asked if they could make these points a little more clear for users on the Knowledgebase page - it may be obvious to them, but not obvious to us, waiting to hear what’s happening.