Attacking Bitcoin service and asking ransom in BTC doesn't make sense to me because the attack itself hurting Bitcoin and it is reducing the value of the ransom, we will definitely see exchange value drop if such thing would become common.
sorry, maybe you're viewing it from the wrong angle.
Just consider how racketeering works in real world.
It is present in all areas where there is a "community" (the mafia) which claims to be in power and demands some control over all proceedings. Any newcomer not actively searching association with that "community" is threatened and hurt and put under attack in various ways. This may go on for quite some while, until the healthiness of the newcomer is gradually drained, up to the point where he's willing to accept "help" by the "community". In a significant fraction of the documented cases, the victim isn't even aware that he's a victim of racketeering.
So, to put that into context, we shouldn't expect the goal of those extortions to be a one-off payment of 1000
BTCIt is easy to keep up DDOS for as long as you want, and its hard to impossible to keep up an internet based business against ongoing DDOS