Soft starters and VFDs have been around for approximately the same time.
They are different devices for different applications, although you can use a VFD as a high-end soft-starter and soft-stopper. But since the price difference used to be so high, this was extremely rare. I have only seen it once. What I am saying, is that in the past you would not see VFDs being used where softstarters could have been used instead. So the scenario you describe does not exist IMO.
As for any new development in this area I would say that both soft-starters and VFDs are becoming more prevalent due to their dropping prices. But I definitely do not see a trend that soft-starters are being used in place of VFDs. Since VFDs are dropping more than soft-starters (relatively speaking) I would guess that it would be the other way around. Especially since you can get STO with most VFDs nowadays, that is an easy and cost effective way to achive a high safety Performance Level, and you dont have this feature with any soft-starter.