I think the problem for MorphOS Mediator support is twofold: its a closed system, Mediator has an 8MB transfer window limit.
Yes, I know - but as far as I understand, the "DMA-workaround" is not used for all cards. For some cards, a Voodoo3 needs to be installed, but for others (e.g. RTL8029 10mbit Ethernet) not.
For the latter "non-hackish" way, driver support with OpenPCI or Mediator 68k drivers under MorphOS should theoretically be possible. As far as I remember, early MOS-version had Mediator support to some extend.
I would really be happy if there would be some way to run at least a 8029 ethernet card with Mediator 68k drivers under Morphos Powerup.
I still wonder about OpenPCI Mediator support - why do they state on their website that it's "100% done", but I haven't heard a single person reporting that he succeeded to run a Mediator-device with OpenPCI?