What options are there for replacement upper/upgrades for the AR-15?  What I'm referring to is an upper like the ZM weapons/ Olympic Arms OA-93 that uses an improved gas system, and a different handguard setup.  Don't get me wrong, the AR15 is a tried and true system with many years of reliable service, it seems that other system, some dating back 30 years have progressed beyond the technology used in the AR-15.  
(Please do not send me hate mail with accusations of heracy)
Has anyone come up with an affordable upper receiver upgrade for the AR I haven't seen?  (I have been very busy these last few months)

I'm looking for an upper with the following features:
A:     AK47 or AR-18 style gas system (with a piston actually separate from the BC)
B:     Easily removable barrel that doesn't require a qualified armorer to install and remove.
C:     Free float handguard that doesn't require a qualified armorer to install and remove.
D:    Hardpoints on the handguard much like the HK 36 / HK UMP
E:     Hard anodized aluminum upper receiver with weaver rail
F:     Chrome lined barrel and bore

Is there anything like this that can be purchased for less than an arm and a leg that's  made by a respectable manufacturer known for reliability and quality control?
Thanks
Tex78