Re: What necessary changes should be made to BP themes for BP 1.2.6
No, any new template tags will not be recognised by your 184.108.40.206 installations.
I’m dismayed by the 220.127.116.11 -> 1.2.6 decision making – with users unable to use 18.104.22.168 themes on 1.2.6. You’d expect some new features in a minor subversion upgrade, some additional template tags you could take or leave, but not for the behaviour of key regularly used functions to be changed overnight (e.g. the multiple friend button issue).
It’s been an issue for us with how on earth we can handle existing bespoke client implementations, but you raise another problem for generic theme developers – you’d have to have two versions of your theme.