Just my opinion, but I see little issues with 1.0.5 and eventually 1.5.x will rule. Would the effort not be more appropriate to 1.5.x and then to back-port to 1.0.5 anything that is "critical"? I run 1.5.x on the UNO and Mega fine (and Pro Mini and Nano) and without issue. But for Pro Micro (Sparkfun), I have been using 1.0.5r2. I was successful in using the Attiny core (tiny85) with 1.5.x, so I've moved that profile over, too. My belief is that 1.0.5 is drying-up on the vine.
Ray