Yes, Capital ships still do jump in. A couple of weeks ago a war started in a system between rival small powers and two Capital ships (one from each side) jumped in as part of the new Combat zone, it was very impressive to watch as I hadn't seen this before.
We were tasked with helping to force the enemy Capital ship away, which we managed briefly by disabling its [Classified] which forced it to withdraw from the battlefield. it returned later though.
I was amazed that the Capital ships weapons appeared to have a range of around 8 KM, that wasn't great when trying to get close enough to one to damage it with my own ship's weapons.