Let's take a page out of Marketing 101.
Sell one device, entry level with no upgrade potential. It comes out fo the box ready to work with games onboard. It has a card reader or other device to allow more games to be purchased. This would have fewer connectors and be perfect for someone wanting to just play games
Now sell another device that can be upgraded. Perhaps there can be two of these, but right now, I would image just one. If allgoes well, release an AGA compatible one.