Doomsday Engine

It depends on which areas of the Doom community Deng Team want Dday to appeal to.

There is dedicated sub community of speed runners and demo recorders. Currently PrBoom+ seems to be their choice of port because of its features (i.e ability to imitate different versions of Doom through its compatibility levels) and ability to run Vanilla Doom format demo’s.

I haven’t really looked at PRBoom+ to any degree, but it’s my understanding that PrBoom+'s demo format is an extension of Vanilla Doom's and Doomsday's upcoming game rules system might allow it to ape some elements of PRBoom+'s compatibility levels without much extra work.

Doomsday is (well, was, as demo recording is currently disabled) still the only port to this day, to offer in game demo recording and playback (even PRBoom+ still uses the command line), though ZDaemon offers the cool ability to fast forward and rewind demos during playback.

Also, Doomsday, unlike PRBoom+, offers support for games other than Doom.

As vermil suggests, the only port that anyone interested in demos uses currently is PrBoom+ and that is because of the extensive work done to precisely emulate a half dozen different playsim variants. To even be relevant in this sphere we'd essentially have to replicate PrBoom+ in its entirety.

On a technical level, its not "just" a matter of using an alternative playsim; we'd need to use the original BSP for the playsim, the original blockmap, etc...