I found an alternate solution after chatting with the premier desk. They found me to reroute via TPE, so the new segment stands (Instead of SIN-LAX original),
SIN-BKK-TPE (using 35K miles with $16copay) all business on THAI, then TPE-SFO (new United polaris business)-LAX, I paid the difference as it was only $1000 more to upgrade from my original ticket price which was $1940, but I get $350 copay back with my 30k miles for the original MUA request on the U fare from SIN-LAX.
Also what I observed on the seating configuration for business class before and after changing my route-there were 26 occupied seats and 22 open seats on the 787-9, as soon as I changed my itinerary from this route it indicated 25 occupied seats instead of 26, although the seating map is not an exact guarantee of the seat availability at that moment, I tend to believe my MUA upgrade request would have cleared at some point even there are GPU requests ahead.
But I am not excited to experience the new polaris business as my in bound flights to SIN, I will be on Lufthansa and Austrian Business class.