The eBay listing says that the project was a spinoff of 3com 3Server so it doesn't have *anything* to do with the "BigMac". (The listing even says the case *is* a 3Server case painted white with an Apple faceplate on it and a couple nonstandard ports on the back.) The 3Server was basically an early NAS device, running file and print server software on a customized version of DOS. Undoubtedly the "MultiServer" was essentially the same thing with an AppleShare software module and a Localtalk port grafted onto it.
The Apple ads that came out in the 1988-ish timeframe heavily promoted the idea that you could add Macs to your office and have them "get along" with your PCs easily. (Touting features such as the DOS-compatible "Superdrives".) Given the pressures of PC compatibility I can see how they might of thought a dedicated cross-platform file server appliance would be a worthwhile product to have on the market before then. (It would be interesting to know when exactly the "Multiserver" project was green lit and subsequently ditched. My guess is that it got caught up in development hell and it became clear that by the time it was going to be ready it made more sense to just sell Mac II's as servers instead.)
The Apple ads that came out in the 1988-ish timeframe heavily promoted the idea that you could add Macs to your office and have them "get along" with your PCs easily. (Touting features such as the DOS-compatible "Superdrives".) Given the pressures of PC compatibility I can see how they might of thought a dedicated cross-platform file server appliance would be a worthwhile product to have on the market before then. (It would be interesting to know when exactly the "Multiserver" project was green lit and subsequently ditched. My guess is that it got caught up in development hell and it became clear that by the time it was going to be ready it made more sense to just sell Mac II's as servers instead.)