[popcornmix]

So what's your intention ?
- Try to improve both as much as possible, and see which one is the 'winner' in the end?
- Try to make DvdPlayer good enough so we can abandon OmxPLayer completely?
- Keep OmxPlayer and DvdPlayer concurrently alive for respectively non-dvd and dvd-playback?
- Backport dvd-playing fixes (e.g. static menus) back to OmxPlayer?
- Other?

There were two main reasons for getting dvdplayer working.
Software decode for unsupported SD resolution codecs (e.g. msmpeg-4, DivX 3, sorenson spark)
Full DVD playback with menus

The second requires the hardware accelerated omxcodec.

There was a hope that if dvdplayer+omxcodec was the "winner", then support for omxplayer could be dropped in favour of supporting the smaller omxcodec.
It looks like that is not going to be the outcome. As omxplayer offloads a lot of the player code to the GPU, dvdplayer will always have a performance disadvantage.
While I get decent performance from dvdplayer with moderate bitrate 1080p, there are dropped frames, and it's not even close to playing raw Blu-Ray rips.

Also omxplayer can play 1080i content well, producing 60fps deinterlaced video output. When you bring up the OSD it is updated more slowly (e.g. at 10fps) which works quite well.
dvdplayer in the same situation has to update the OSD at the video framerate which results in a lot of struggling.

There will be improvements possible to dvdplayer+omxcodec, but I suspect not enough.

But I'd suspect a significant number of users don't play much 1080i or Blu-Rays content. Most of the content I watch is 720p and plays pretty well with dvdplayer.

So having the choice available does mean if you find a problem with audio sync, or subtitle sync, or smoothness, or tolerance to errors or bad timestamps, or an unsupported (SD) codec you can try using the other player to see if it behaves better.

At the moment a goal would be to:
make dvdplayer the default for dvd images
make omxplayer the default for all other files
allow "play using dvdplayer" to be a manual option for software video decode of SD codecs, or as an alternative for a file that plays badly.

Unfortunately xbmc's structure doesn't make it easy to automatically play an unsupported codec with dvdplayer.
You only know for sure that you can't play it once omxplayer has opened the ffmpeg demuxer and got the codec hints out (the filename is not enough).
It would be quite ugly to make omxplayer return an error and then have xbmc retry with dvdplayer (but it's an option).

A longer term goal could be to merge omxplayer and dvdplayer.
Currently OMXPlayer.cpp and DVDPlayer.cpp are quite similar, so use a common file for that.
Once ffmpeg parsing is done either code from DVDPlayerVideo.cpp or OMXPlayerVideo.cpp would be invoked based on codec/resolution and user options.
That would avoid some of the maintenance omxplayer requires (merging changes from DVDPlayer.cpp to OMXPlayer.cpp) but shouldn't harm performance.

Backporting dvd menus to omxplayer certainly would be nice, and having spent a long time debugging issues, I am in a better position to do it, but I'm still not confident I'll ever get it working perfectly.
There is a lot of very hacky code that does this. dvdplayer doesn't even use ffmpeg for decoding the menu's videos, but libmpeg2 because they couldn't get ffmpeg to behave exactly as desired.
Using omxplayer, with the decoded frames not even visible to the arm makes this much harder.