iMessage worked because everyone got it. Catch 22 for Babel.
The great thing about Android is how google updates its apps outside of an actual OS update, however from the looks of things Babel seems like a major overhaul of the entire messaging system, probably from a server to notifications level deep in the next OS update.
What this means is if we look at the best case scenario where google release an app on the Play Store for 2.2 and above than Babel becomes another WhatsApp, KIK, Schat etc.. but people would already have whatsapp and see no actual advantage, it will become a game of telling everyone you know to stop whatapping and start babeling, the people who have experienced this are well aware that noone moves chat platforms for you specially if they are girls who just post pictures of themselves at whatever outlet they find, in other words this thing needs to be way more than another whatsapp.
G+ - Seeing as how noone really cares about G+ and it already has apps, but lets say google discontinue G+ apps and replace it was this, somehow replacing system built apps (as G+ and M+ come built in) it will still defeat the purpose of being your one hub as hardly anyone uses G+ apps when whatsapp is there and the MAIN point of having one place to SMS, MMS, data message etc is still left out cold.
iMessage worked because everyone who had a 3GS, 4 and 4S, iPod 3rd gen, 4th gen, iPad 1 and 2 all got it, they just got it weather they wanted it or not.
Fragmentation is Android's biggest problem, i've being wishing for a PhotoStream, iMessage and FaceTime type of service on Android for ages, those things above are pretty much the only reason I still Keep my iPhone 4 next to my One X,
There is no point in this Babel if noone but 0000.1 Percent get it.
Lets see what happens.