I fully expect an iMac "bigger" (not necessarily 27") will return. However, I suspect it will be labeled PRO and priced like Apple priced the prior incarnation of iMac 27" PRO.
Apple has successfully launched the iMac 27" monitor at the former "starting at" price of the same monitor with all of the iMac computing guts inside. Logically, when they later add those guts back inside, the new (improved?) price will reflect the addition. I approximate that by looking at MBpro pricing and then subtract something for the parts that wouldn't go inside (screen, speakers, camera, etc) since they are already there. My best guess is an iMac "bigger" with a "starting at" $3499.
If Apple really pinched the base configuration and made keyboard and mouse accessories instead of "included" (as it used to be), MAYBE that gets down to $2999. However, I suspect the "nicely configured" versions above the "too little..." specs is probably NORTH of $4K.
In all these threads dreaming of a return of the 27", I suspect a driver of that dream is former (relative) "bargain" pricing. I'm not so sure the market will be as receptive when the new one does arrive at much higher pricing than the traditional level. Again, now that ASD is established at what used to be a whole iMac 27" price, I see no way for iMac 27" or so to return at former price points.
For OPs situation, I mostly agree with post #10: pair a Mini with a third party monitor. If so, I might wait a bit longer for the debut of the Samsung Viewfinity S9 to see what that 5K monitor will cost. If Samsung doesn't demand so much margin, that may be THE best choice to pair with any Mac desktops.
Also consider the LG that was formerly endorsed by Apple themselves by being
THE 27" for sale in stores until ASD. Apple fans have dramatically turned on it since ASD launched but it was apparently just fine when Apple was pushing it themselves. It can be had for a LOT less than ASD and performs just as well as it did when Apple was pushing it and thus fans liked it.
#10 is right that a 4K screen will cost a LOT less than the oddball 5K and with some screen config choices, OP can probably find a setting that looks good anyway (try hooking any Mac to any 4K TV and the result is not the "terrible" often spun in support of "5K and only 5K" arguments). If so, a 4K monitor also unchains the choices from 27." For example, perhaps 30" or more... and maybe ultra-wide can come into the consideration?