Something that has been bothering me about the trail renderer since forever is that it always simulates in world space. If you want to add a slash to your character’s sword, it’s going to be affected when you move around. You’ll have to excuse me if it’s not the right place to post this, but I figured that since the TrailRenderer is being worked on in the current beta that it might be a good idea to request this feature here.
Is it something that is planned to be added during the 2018.2 cycle?
It’s on our roadmap, but you’re right that it’s not the right place to ask this 
Here would have been better: Unity Engine - Unity Discussions
It’s not planned for the 2018.2 cycle, sorry!
Got it. Thanks!
Is this still in the works? It would be great to have the option, just like the particle system, where in addition to local space, we can designate a custom transform as the simulation space for local space.
Hey, it’s not being actively worked on, but is on our internal roadmap, sorry!
Is there any news on this? I have some trails in a sphere and I want to rotate the sphere and preserve the trails that I have rendered, any idea how to achieve this?
Hi, sorry, not really… Maybe you could do it with a Particle System?
I highly recommend writing your own trails or using a third party asset. Unity’s trails have been long lacking in a number of features, most of which I would not really expect to see much future work on any time soon (if at all, though @richardkettlewell can answer that better) as most of their focus is going to be on the new VFX Graph and SRPs going forward.
In the past I’ve used several in-house trail systems, but since leaving the company I worked on that code at I’ve been using Ara Trails and been pretty happy.
Correct. The trail renderer won’t get any feature work - it’s old and slow (one trail per gameobject is not performant).
VFX Graph has recently added trail support. And even particle systems can do trials, in both local and world space.