At this point in time nobody knows. I suggest checking this page once in a while for any updates. It has a direct link to the download should it become available. RTX 3000 series Vbios links 
Hello,   When can I expect a vBIOS update for the RTX 3090 that includes the feature "Resizable Bar." I see that it may have been released before, but it is no longer available. Please respond accordingly.   Thanks,   Panasonic
Release date of RTX 3090 Resizable Bar support update.