For those doing point to point staying in T1 until they shut it down would have some advantages, a nearly empty airport and closer to central London - 15 mins HEX, option of the connect, served by both the T4 and T5 tubes.
The few fond memories I had of the old T2 was when most of the other airlines had moved out. I had a couple of flights from there when LH/LX had moved out and it was such a different experience going through the terminal (the place was still a dump though and the AF lounge was dreadful).
Still for most people this will be great news, particularly as it sounds BA are doing things right and increasing the number of domestic capable gates. Connections will be a whole lot easier, particularly from BHD, no idea who they'll do flight connections from DUB.