Well, Xemu is just collection of some "random" emulators, actually MEGA65 is just one, and even much more new kid in the family than some of the others
Xemu itself is not MEGA65 specific as a whole. But I can understand why people think otherwise
Even not Commodore specific btw ...
Yes, emulating an external drive can be a solution, just it must be written
Which is hard with the current precision of that emulation target, as IEC bus implementation need precise timing, and you also need to emulate a disk drive in addition of the computer itself. That's why there is no such a thing for other Xemu emulators either, including MEGA65 (where you can use the IEC bus to connect even an 1541 in theory ...).
The problem with your theory to re-use code, that C65 and MEGA65 internal disk drive is easy to emulate, as it's just a disk drive can be be accessed directly by the CPU of the given machine, so you don't need to emulate the working of the IEC bus, and a whole second computer (as a commodore disk drive after all is a full computer, with ROM, RAM, CPU, I/O chips ...). Yes, well, maybe it would be easier to actually implement Commodore LCD emulation inside the VICE project, since it already has got mature emulation of external disk drives
Even just emulate a "dummy drive" (like what SD2IEC does as well, ie not emulating the internal working of the disk drive, only it can speak the IEC protocol ...) requires at least "speaking" the IEC protocol. Honestly I've tried once, many years ago, but I always found that it's too much for me, to ever understand how IEC protocol works, it's just too weird for me, also maybe timing issues was a problem as well, I am not sure. But otherwise you're absolutely right, an emulator is kinda useless if you can't even load/save from/to the external world ... :-/ A generic IEC implementation in Xemu would be very useful, for many emulators, not just CLCD but C65 and M65 as well! In fact even non-Commodore emulators inside Xemu would benefit (for example both of Z80 based Enterprise-128 and the Hungarian primo had interfaces for IEC optionally, in fact Primo - at least some models, not all - has even built-in by default, though missing ROM code to actually use, so you must load the software for it first ...). Also, the IEC implementation could even help to add "printer emulation". Etc.
Yes, compared to Commodore LCD, C65 is a very common and easy to buy machine
According to Bill Herd, maybe 4 or 5 units exists in total (he has one, but he even not dare to power it on in the fear to blow something up, funny, once he wrote me, that if I will to sell my house, maybe I have enough money that he at least consider to sell it to me ...). The number of produced C65 units at least in the magnitude of hundred, if I'm not mistaken.