Another option would be something like Peak Pro's "VBox" (TC Works had one for Spark back in the day as well) that gives you a plug-in routing matrix as an insert.
The Spark thing also worked as a plugin, AFAIR.
Anyway, modular hosts also working as a plugin (Bidule for example) allow for just the same thing. But it's not exactly easy to deal with them (no quantum physics, either, but still...). And in addition, you can just forget about all of Logics internal plugins (which is a shame generally, but that's probably quite another story).
When you think about it, parallel FX could make a lot of sense. Even in the synth department. I still remember my Windows days pretty well. I was running Energy XT as a subhost instrument plugin, happily layering all sorts of synths in just one audio object. More or less absolutely impossible in Logic (I know you can layer synths but that means quite a loss of comfort).
Especially with something such as the EXS (which, unlike, say, Kontakt), which doesn't allow for any layering (unless you combine two patches - and "awkward" would be a blatant understatement for that procedure), something like that would be perfect.
Also, you could save your creations as one single channel strip, yet something else being impossible with a multiple aux/bus routing scenario. Also impossible with environment instruments that you need to properly layer virtual synths in Logic.
Really, almost anything could benefit in one way or the other.
A nice idea would probably be to a) offer some audio routing inside the environment (something seriously lacking anyway) and b) offer access to this routing via a plugin (think modular hosts).
The environment could offer out- and inputs for each insert, then you'd just happily cable around. Perhaps not the ideal "quick access" solution (which is what most Logic improvements seem to be all about these days).
Alternatively, a switchable channel strip would be an option (so one could chose from a variety of inserts shown in a variety of fashions, heck, there could even be a "wide" mode or something).
Anyway, there's a whole bunch of situations when one would profit from such a function.
- Sascha