They are going to manufacture sound cards.
No, it is a decoder card, akin to MAS-player, not a sound card.
And maybe they don't want to undercut their OS4 market.
What market? Hardware to OS3.x does not in any way, shape or form, compete with OS4. The issue is more that a Minimig+ would require someone willing to develop the FPGA code for it, and I can not think of anyone who would want to do that exclusively for them. The best a Minimig+ could hope be today, would be a MIST clone. But we already got MIST.
Further, if Jens has most of the supplies of OEM chips, CLPD or FPGA based parts would have to be substituted (not that that couldn't offer some room for improvement.
?? OEM chip?? Jens has most of the supplies of the AGA chips, these are not at all needed to create new motherboards based on FPGA.
Finally, A-cube announced a new version of the MiniMig awhile ago, and while that has still not surfaced, does A-eon want to tread on Acube's market?
What? It was A-EON who announced the Minimig+ with A-cube as a partner. But neither of them have developers to actually develop Minimig FPGA core for such a board, all they can do is to develop a board for which there already exists some rudimentary support, and hope it attracts developers. That is how it works, and it does not fit "business plans" of these companies.