Well a bit of history. The number one problem with DCC is maintaining the fidelity of asset with in the creation pipeline so that in what is in one environment works in another so is yet another reason to stick with an all Autodesk pipeline as even FBX belongs to them so of course it supports most things 3ds Max as a container so the data is there it’s just that Unreal 4 can not make use of it. (more on that in a moment)
So to make use of PCD it’s not an issue of coding but one of patent licensing of an engine that is now open licensed. (AKA not open sourced but rather fair use licensed) and since everyone has access to the engine code, which would included the PCD block, Epic would probably have to pay a license for every download seat. (I’m guessing of course but have a good idea of how stuff like this usually work)
That does not mean you can not make your own PCD pipeline by starting with the fundamental of just how PCD works in the first place by solving the problem.
PCD at it’s core is a series of progressive morphs stored in sequence much like an AVI is in theory just a string of indexed images and the PCD modifier packages the progression with in a single data file. What we do know is UE4 “does” support individual channels and so does 3ds Max so we have the means to build our own, but limited’ vertex based animation system.
A way to do it would be to set up whatever means you wish to create a real time deformation with a morph modifier on the stack of the target object. Stepping the track you would take a snapshot in the morph modifier into individual channels as a progressive, being sure to change the name of the object each time you take a snapshot, and the modifier will store the vertex data for you. You would repeat the process for each frame you wish to capture until completed. Keep in mind that 3ds Max only has 100 channels available and you can not stack channels.
Once done you now have an object that contains the necessary data to behave as a progressive data package much in the same way that the PCD modifier with but in an automated manner and once exported would behave in the same manner as want object would that contained morphs into UE4.
From there you have more than a few options. You could make your own sequences or even use 3ds Max to animate the progression and export the animation along with the target object.
Something to keep in mind though is vertex based animation dose not have a local transform as it’s the vertices that are moving and not the object it’s self so using it as a train will probably not work as the object will remain fixed as to it’s local transform, so you might have collision, a player standing on it would not go along for the rid.
PS is’t been a while so there might be a better solution but the big one is morph targets are now hardware rendered and no longer has the performance hit that they use to.
After thought you could look into Alembic as an option to export vertex animation. UE4 supports it and the more recent versions of 3ds Max has export support but I’ve not looked into it as I have no need to spend update bucks.