The imx8plus is basically discontinued and so suspend attempts there are not happening .There was, however, a pseudo suspend script which tries to power down as much stuff as possible. It is a good solution for now.
I think most suspend efforts are going towards the RK3588. In recent talks with Josch I found out that it is technically possible for the A311D to suspend. Work just needs to be done for both SoCs to get that functionality integrated here.
Like you I would very much prefer hibernation as well.