Not many successful cast aluminum 1911 frames out there, actually Ruger makes the only one I know of anymore. Most aluminum 1911 frames are either forged or machined billet. Some will remember the issues with aluminum semi-auto pistol frames in the 70's and 80's, even some very good manufacturers had some major problems in the field.
As for a polymer framed 1911, the trigger group/mainspring design would have to change so much, it would not be a 1911 anymore. You might be able to make it look mostly like a 1911 but the parts would be very different and not interchangable with real 1911 parts. I don't know many 1911 guys that would go for that.