I think Quadrantals will disappear anyway pretty much, as they only apply up to FL190, after which it's the semi-circular rule already. When the TA goes to 18,000ft, that leaves only a small band applicable to Quadrantals, it would probably be sensible to get rid altogether.
They're pretty much a waste of time anyway as far as collision avoidance in IMC OCAS goes, much better to just let people spread out randomly at various altitudes.