What behavior were you trying to get it to do? If you were trying to make it so that it switches tabs in the tab strip order (instead of recently used order), there is a setting for that:
Opera Menu | Settings | Browser | Uncheck the box for 'Cycle tabs in most recently used Order'.
I thought there would be since there is a 64 bit edition for Linux
It's because you can't run 32 bits programs on a 64 bits Linux. Or, at least, it may not be that simple as in Windows.
Can you tell if this lack of ETA is due to no-one actively working on it
Nope, it's because this is something new that needs to be tested and reach a stable state before go to the stable channel.
is it safe to assume that it will eventually reach stable channel?
It will, most probably. But it may take a long time.
And, is the developer one compatible to the stable?
It's not advised to copy from stable to developer. Best option would be to enable Sync on both.