If hive was to fail / crash in token price – is it technically possible to move the POB platform over to somewhere else, to another blockchain, quickly?

It is technically possible, but currently there is nothing along those lines set up.

Is it possible to refuse the rewards on Hive, but still accept them on Proof of brain?

Not currently, but if there was enough demand for this, it is doable

Is it possible to ‘subdivide’ POB into more niche threads?
IF it were possible to tag into different sections – I'd suggest limiting the amount of tags that can be used.
Strictly.

While this may seen counter intuitive at first glance, it isn’t…
More precise, and limited, tagging , makes for a far superior user experience.
(e.g just because I mention in passing, 'bitcoin is crypto’ -it doesn’t mean that it qualifies to be tagged in leofinance, now does it?)

This is a good suggestion. Maybe we should limit it to 5 tags that are actually descriptive of the post and not just hive-engine tags. I everyone started doing this, it would make the most used tags much more useful.