Would it also be possible to show layers with their corresponding assigned layer colours in the selection filter dialog?

That should be the case indeed (only if hierarchical layers are enabled).

Ha, yes indeed when hierarchical layers are enabled - it works, apologies.

Yes, the hierarchical layer list is basically just the new layer list with hierarchies, colors, etc.
Eventually, it might replace the old one completely.

"Eventually, it might replace the old one completely".
I think it should replace the old one, its much more useful.

For new QCAD users, the hierarchical layer list is the default starting with QCAD 3.4.4.
However, I know from previous experiences that many users find it hard to cope with change and prefer things to be the way 'they always were and worked before' ;)

Yes, fair comments Andrew.