Neither EA nor V1 supports Terrain as such - the product and the way it is designed from the base up never intended that terrains should be inserted.
The official statement regarding EA was that you could place Terrain but not walk upon it.
During V1 beta develpoment when Physics was eventually included I was the prson who first tested it out with terrain and it worked fine though at that time I never tested out any enemies in the landscape. Between then and V1 release the product changed anyway and and so you have what you have now.
Terrains and and any other game element that the engine does not support by default are always going to be very difficult to get to work in FPSC properly and are likely to prove to me more hard work than the worth of it in many instances - with at best poor results being the end result of a lot of effort.
Attempting what the engine does not support is fighting against the basic understanding of the source and is sure to cause all kinds of problems. FPSC has enough of those even if you stick with what its supposed to do and support by default.
Terrain at least can be inserted so users are half way there.
Currently users can move ahead designing levels using Terrains and hope any update may fix some of the issues associated with them by accident or design.
Its perhaps likely that at some stage at least changes to the engine will in any case provide overall much better support for terrain or mess its inclusion up altogether.
No one knows what any update may bring and how it may affect your current level design and influence your current developments.
Hopefully it will be fully backwards compatible, then again if thats at the expense of badly needed improvements I personally would rather see an improved product and live with any incompatibility and put in extra work to update any current game levels to fit in with any new internal engine workings.
As to Terrain support itself it seems that if TGC did some work on the NPC characters and other entities recognition for Terrains then that alone would solve the main problem if no real Terrain engine support were to be inbuilt by default.
Not sure anyone could rely on that as I am not sure that it has any priority at all - I presume and have no reason to suspect any different that FPSC is still seen by TGC as a FPS internal shooter game maker so they are unlikely to worry to much about Terrain support - indeed before considering that they in any case have many other important issues to consider such as improved collision which would also be an aid to Terrain support itself.
"I am and forever will be your friend"