Funny you should mention those.... I have been working on making a dumping program for the PC Jr. I have managed to read cartridge data and dump the hex to the printer, but I haven't had much success yet with saving the data to the disk drive. Anyone who is an expert with FDD accessing, please help me!
As for Game Genie... I was thinking about that recently as well. It is possible to do, but will have to be done through a modified BIOS. One of the 4k banks of the BIOS is empty, so that's plenty of room to put a GG menu in there. Maybe I'll work on that soon too.