Well, I am an MS25 user, I was on Live before and now I am again... still works.. however, I am not too sure whether this is a safe way.. yes, MS28 might have a FirmGuard but MS knows my console serial number.. maybe they would be able to find out "okay, this console is a March 2006 console before MS28 was invented so this drive shouldn't have a FirmGuard" - in fact it has, boom, I am away.. only speculation in my eyes but possible (being online with a pure MS25 would be probably also dangerous: dump firmware, check, boom, away)...
let's hope M$ is not able to find out the console or drive date - if they can, I guess MS25 users will be their target - MS28 users should be safe.. their firmwares have firmguards and as firmguard exists Ms will probably be unable to find the banned drives!