I think we see this phenomenon all around the world.
Bigger companies take over smaller businesses and grow even bigger.
Being the biggest in a country is not enough anymore. Big companies need to be big even internationally today.
But you still see the specialized, local shops in the villages and towns all around the world.
Same with the forums vs. social sites like Facebook and Twitter.
The biggest threat to Facebook and other social media is the fact that they do not have a niche.
The grow bigger and bigger and loose the meaning of the site.
I agree the social sites are very useful for many people, like myself for example.
I live in a country 8500 km from my relatives and friends. I use FB often. But its more a means of communication.
And therefore the biggest upside of forums, is just the same. Niche.
A forum today, with a strong niche and the market for it, will beat FB and any other social site easily.
So in my opinion you cannot compare the two.
It is like comparing a phone or email to your hobbies, interests or passions if you will.
Yes, this would greatly improve the splitting system.
Many times on my board I would like to split a topic, but with page after page of "ticking" off topic posts, this seldom happens.
It should be only one click and select "split all posts after selected post". Done.