Short answer: Here and now, no.
Long answer: It really depends on how "transparent" these devices are with respect to the cartridge contents. For the SGB, for instance, the SNES only sees the 256kByte ROM that constitutes the Game Boy border. The Sega Power Base might be a different story since Master System carts plugged into it are actually processed by the Mega Drive/Genesis, so the cart ROM must be available through the Genesis slot somehow. Still, in order to add support for it in the firmware, I would need to get my hands on such a device. On the other hand, I am trying to come up with dedicated plug-in adapters for the Retrode that would allow for the insertion of other games. Atari 2600 is already working okay for some games (schematic is online, so get your prototyping breadboard and a handful of wires and you can easily build one), and N64 and the Game Boys should be next once I find an elegant solution for managing the different voltages. Once the Retrode has a certain user base, and if some programmers out there are interested, I might consider releasing the source for its firmware so anyone can add new features.
Sorry, but there's not much I can do about your worthless currency As for the price, developing the Retrode and bringing the hardware to its current state wasn't actually cheap, and of course the production itself ain't free either. I already had a lot more made than I should have, in order to get the right connectors and at least some volume benefit. Anyway, as long as I am sitting on the first batch, I cannot guarantee that there will be a second one.
Then again, I think with the Retrode you really get a lot for your money. Just add the cost of two flash cart programmers (Tototek / Mash-Mods), and you're already way above the Retrode's price. And these things are much more of a pain to use, unless you're into command line tools, printer port data transfers, proprietary drivers for exactly one operating system, autorouted circuits with sawn-off connectors, and the likes. But, you know, that's just, like, my opinion, man...
Cheers,
Matthias