As much as I'd like this thing to be there as well, there are two significant challenges to getting this feature properly done.
First one is that each object that can either exist or not causes a little bigger performance hit vs an object that is completely static, in RWR.
Having just certain fences or oil barrels, rather rare stuff like that, destructible might just be within a reasonable range for not ending up with a too big performance hit. We need to keep in mind that people are playing RWR with lower end PC's as well and are already struggling with performance.
The second challenge is the AI. The AI can handle steering around isolated disappearing objects like crates (pretty similar thing as an oil barrel), just fine, no problem with that, but the system made for navigating around/over longer wall/fence lines have been made to only support a static gapless model. So, going down there in that maze of code that does that and improving it to handle dynamic walls, it's a bit intimidating at this point

Curiously enough, we are actually adding a single destructible piece of wall in the second final boss map, and the AI barely handles it thanks to a hack I was able to pull off. It isn't perfect, but seems it works fine enough at least for that particular case.
Basically then, the pieces of fences and oil barrels too could be now modded to be destructible, the support is already there in 0.98.8, it's just we have no real data about how much it affects performance and if the AI gets confused about it when used all around the place and seems we won't have time to study it before 1.0.
The support is of course delicious enough that we probably will see it become taken into general use sometime after 1.0.