Any solution requires both you and third parties to work together, even if it just means you giving them an API to write their stuff to. If you don't put out the olive branch then the userbase will continue to throw your scsi.device in the trash.
But that is exactly the problem: There is no API at the scsi.device level to get that supported.
That is exactly the point, numbnuts. There is no API for scsi.device right now.
However: YOU ARE A DEVELOPER. YOU COULD MAKE ONE.
That's all you would have to do. You don't have to include OS support for IDE splitters or buffers, you just need to provide an API for third parties to develop this support themselves.
99% of the functionality the third party hardware/software provides is now in your updated AmigaOS. All we want is a safe way to enable the last 1% ourselves. Otherwise we have to throw away your 99% and your endeavour was pointless.
As it is this is my compromise argument, where you don't have to support any hardware you already don't, just provide a new (and rather small) API. But as kolla points out your arguments against actually supporting such thirdparty HW is bad - you say there's no specs and it can't be tested properly, but it's all documented and implemented by everyone else 100%, so it's obviously not that hard. "I don't care" is not an adult response to being proved wrong.