No. We've been over that in the related HD20 link referenced above. That's the whole idea here to ultimately replace the failing and increasingly rare proprietary HD20 Rodime hard disks, not to mention giving the 128K a hard disk option it can use.
When you say hang a disk from the serial port, that was the recommended method by Apple. However, third party companies immediately saw the advantage of using the floppy disk and they along with Apple offered solutions, some for the 128K. The HyperDrive took another more destructive path attaching directly to the 68000 chip, which also required a 512K RAM upgrade. All of this was contemporary to 1984. Bass' solution is elegant as well as being a contemporary solution, not to mention simply adding SCSI to the original Macintosh which lays most of the groundwork for taking advantage of those methods to which you allude available to the Mac Plus onward (Actually the 512Ke can use a commonly found commercial SCSI board in conjunction with the 128K ROMs to add SCSI functionality). The greatest challenge on this board is that there seems to be very little 68K programming going on as compared to other boards like the Apple II. Therefore, we need ready made solutions like this which can be more easily be tweaked to meet our needs in the absence of a dedicated software engineer. Adapting the HD20 interface to accept a flash drive would likely be a significantly more substantial project, even if someone went to the Stanford Library and were able to find the original HD20 documentation in the Apple archives, not to mention it would not return the numerous benefits of SCSI. With very few exceptions, if they only had more RAM, there is nothing the 128K & 512K can't do that the Mac Plus does, except SCSI.