While I was working on #8247, I was testing a lot of blocks, including some that have Block entities that are currently not allowed as facades, and didn't notice any problematic issue with them.
In fact, except for the ME Cable and / or Bus (which crashes trying to render the facade of a ME Cable and / or Bus...), all blocks I put into facades behaved fine, falling in anyone of the following categories:

• rendered fine, about what one would expect from the block (e.g. ME Drive)
• rendered, but with lots of z-fighting (but also expectable from a 3D model which got flattened) (e.g. wireless access point)
• didn't render at all

I'd like to add a config option that blanket allows all BEs (which are otherwise permitted i.e. they are full blocks)