Ahh... ok then it makes more sense. =) I was thinking you found the perfect hardware provider.
I also love ZFS but to be honest, not the future for me. And you probably know that on these things you wanna balance the amount of features and how easy is to play with something. I agree that Synology hardware is usually rubish for what I demand... but the "easy" way of playing with their customized busy box is just very intuitive and easy. That was the reason I used Xpenology 5.x until now... plus some SSDs to cache, did really solved 99% of my own problems.
But you clearly looking to something more heavy and in that sense I agree that even Xpenelogy (where you can build your hardware, up to some extent) might not even be for you. Usually one sign of how "far" you wanna go, is how many "competition" you have for the products you are using. If none, then you are going very far. And therefore, tradoffs will happen. Usually complexity for who's used to it, is a great plus because you gain access to a lot of features and some enterprise level stuff too. Otherwise if you are not comfortable with playing with big bugs... then, I would say, avoid the challenge. Especially if all the reasons you are setting up a NAS in first place, are to make your life easier! =)
Please do post about your last findings about this. I would be VERY interested. Even mention me (as I know that way I will have a look). 🤣
Cheers