Yes. I think animation layers are just basically a subset of same thing with just a new set of problems.
Animation layers dont cut it if you want to, repeat stuff, blend repetitive stuff or rearange parts of the animation like a film editor would. Thrax is great if you allready have many many channels of animation readily done and you just want to re coregraph them to make a new animation.
The problem with trax is that trax is not for a simple animator its for a big studio that has a LOT of ready made animations done, that need to be reused. A bit like every known 2D cell animations cut the same scene all over the different weeks. Same idea but on steroids.
So normally its not very popular with the grunt workers. But not with the Owners of said IP, because after some point they nolonger need to animate the things anymore just recombine in different ways.
So trax is indeed not obsolete in fact ist much better than animation layers for most jobs. Juat too complex for most users to grasp,* which tends to limit things.
But for this kind of stuff trax indeed shines. Even if you dilike using trax just glue the anims after each other and release the data back to keys. Done with a gui present to do the job for you.
*its a tradeof complex does complex things simple does simple things. Simple is easy to learn and easy to use. Complex is complex to learn and hard to use but may do things the simple does not.
PS; trax is actually back in maya 2011 with new tricks up ist sleeve like multi camera cutting, sound merging etc.