But then where would the OTA channels go?
E* could get creative with the channel numbering ...
OTA DTV is broadcast with a major and minor channel number for each feed within the DT stream. Normally the major channel is the NTSC channel number associated with that broadcaster (DT35 would broadcast "major channel" 3). The minor channel number usually starts at 1, with the .0 or -0 channel numbering reserved for the analog feed.
A standalone NTSC/ATSC tuner would tune 3-0 in NTSC and 3-1 from DT35 (assuming that it knew that DT35 carried the 3-1 stream).
I'm assuming that E* can tune to the -2 feeds on OTA DTV, and has found some way of listing them in their guide. What they could do is use -0 for OTA NTSC (assuming the tuner is cabable) and the channel with no -# for the remap of E*'s feeds. -1 and above would be the usual OTA DTV channel mapping.
If the receiver is not capable of tuning NTSC then they could simply use, in the above example, 3-0 for the E* feed remap and 3-1 and above for the OTA DTV feeds. Hopefully they are allowing for the -2, -3 and above feeds. They are a major benefit to OTA DTV.
BTW: They should also fix the remap bug that causes stations that transmit out of spec DTV PSIP information not to be displayed. If the "major channel" is known invalid it could be ignored -- using the tuned DT channel instead. That would fix the Chicago area user's problem.