I don't think VSL is worried about anybody else "catching up". I don't think they're going to do anything at all to keep competitors at bay If they were worried about this, they would need to put out an expansion any time any competitor makes any library that's even closely related to an instrument VSL has recorded, since every new library offers something different. We would have a new VSL expansion every three minutes and it would just be ridiculous. Let's look at the facts though. VSL's instruments are what, ten years old? More? And they're still heavy competition for the very newest libraries. In that ten year span, VSL's instruments have been honed to perfection and their sampling methodology has been so fine-tuned that new instruments and software come out virtually bug-free. Also VSL is far ahead of the competition just by releasing something like Dimension Strings. I'm not sure if a competitor will catch up to that any time this decade. Honestly I'd be running over to Orchestral Tools' website posting comments like "VSL is way ahead of Orchestral Tools--we need expansion packs!" because of DS. But OT doesn't care what VSL is doing and vice versa because the libraries are so different and it would be the death of any developer to watch what everyone else is doing and try to match it.
As a side note, the list of expansions and upcoming products that OT has posted is in no way detailed. It's a stretch to say that they're going to wipe out VSL with all these upcoming articulations when we don't really know what those articulations will be. For example, Expansion B of Berlin Strings provides sul pont, sul tasto, harmonics, and col legno. VSL already offers all of these in some way or another. To be fair I'd love if VSL would provide these articulations with legato, but I can't remember the last time I've missed it.