Another route VSL could go would be to identify the specific reasons people are asking for a midi plugin slot and instead just build that functionality into VePro somehow, especially as pertains to articulation management.
That's a fine idea. We don't need our answer, we need the problem solved.
Here's the problem - and I'm limiting it to just being a consumer of ($14,000+ worth of) VSL sample library products:
Whether it's VI Pro or Synchron player, VSL requires more keyswitches/commands to be sent per articulation/patch change than any other product. In VI Pro it was matrix/X/Y, and sometimes A/B switch (4). With Synchron player, the sky's the limit.
VSL has a reputation for being hard to use and this is exactly why. Solving this problem in a DAW or notation program is a lot of work, and every articulation system is different. So not many people do it, and not nearly as many people use VSL as could.
What do I want instead of 4-6 commands per articulation? I want to send a single PC/CC. There are rarely more than 128 patches in an instance, and I'd be happy to live with that limit. Within the instance I want to be able to say PC/CC 42 = this patch, PC/CC 27 = that patch. That's it. I'm not playing this live, I don't want my hands on 5 controllers, I don't want extra keyswitch notes on my tracks, I don't want to have to record keyswitch/CC dumps or anything else. Nothing about solving this need get in the way of also supporting multidimensional live control.
This is what I use MIDI scripting for - turning a single PC/CC into the pile of commands that VSL requires. Obviously this could be solved in the VI/Synchron players, or VEP.
The other thing I always use MIDI scripting for with VSL is making it so CC2 can be interpreted as velocity when VelXF is OFF. That is, I want to use the CC2 value for the dynamic without the crossfading. This also could be supported as a mode right in the players.
In any case, the biggest point is that this desire/need is driven by VSL's sample products themselves. It's not an abstract "wouldn't it be cool" thing. I really don't want to have to use BlueCat Plug'nScript or Logic's Scripter etc. But VSL sampling products are just too cumbersome to use without, IMO.