Yes, it is now possible on many Sony Portables thanks to firmware reverse engineering efforts and custom homebrew code. Most of the functionality is available directly in Web MiniDisc Pro.
Has anyone made any headways into MD DATA itself and/or trying to dump from a portable audio player?
I'd love to see what I can pull from some MD DATA stuff I've got from an old DATA EATA and a Sharp Viewhunter camera that I just can't track down the damn weird proprietary cable for that shoots on MD.
Not yet. There have been some experiments with this in mind, but nothing practical yet that allows dumping data discs. Considering that we have large control over the firmware, it should become possible with more work (and time).
> Web MiniDisc Pro (WMDpro)[0][1] is a web app that can copy (almost) any audio file onto a Sony MiniDisc using the NetMD USB protocol. It can also manage tracks, erase discs, and enable new features that extend the MD format. It is a complete replacement for Sony's SonicStage (except Hi-MD modes.)[2]
See https://github.com/MiniDisc-wiki/md-firmware And https://github.com/asivery/netmd-exploits/