I like the idea of a Natami based cpu accelerator for the A1200 (and possibly 4000). Add on a high speed ide port and you are in business.
Since thats not very practical, a new run, or revision of the IDE-Fix Express. These really need to be available again. I would like to see the 40 pin connectors removed (or become removable) and just concentrate on the 44 pin. SATA would be nice for SSD drives but probably not practical either.
New Indivision AGA 1200 run (or the MKII). Why the hell aren't these available again yet? Its not like they didn't sell like hot cakes or anything. Would be nice to see a better mounting method as they can be finicky to keep secured. Perhaps DVI as well VGA?
External SD/FF. I know the image quality isn't going to be quite as sharp as an internal unit, but installation is brain dead easy and doesn't require modding to make it fit (or to keep it from moving around). While many of us have multiple Amiga's, how often do you have several hooked up at once? Would be nice to have a "portable" SD/FF to use.
A proper aftermarket desktop case for the A1200. Something similar in size to the A1000 or classic pizza box style Mac. I personally don't care for tower conversions, but I do like the fact they allow you to use some of the accelerators that just don't fit correctly (or get too hot) in the A1200. This is something I am actually thinking of working on. Slim optical drive up front (maybe...or perhaps slot in style?) and a place for a floppy drive (perhaps locate it on the side to clean up the front of the case?)