You are in the minority, particularly with your view that aluminum and glass looks more plasticky than the actual plastic of the original G3 iMacs.
No one can concretely say what will or will not look timeless in the years to come. Standards change particularly when you live long enough to see things once seen as ultra modern and seemingly cutting edge when new become very dated, quaint and even clunky.
As I posted elsewhere the previous generation iMac with its silver/black design looked sleek, premium and ultra high tech even as it aged in comparison to the vast majority of PC competitors, yet it took the new iMac design to finally make the old look dated.