Yes, stations moving from (abt) Ch30+ to Ch51 Band to a lower UHF Frequency will need a new Transmit Antenna System. UHF Broadcast Antennas are fairly narrowband when providing very low SWR and typically cover only one or two ADJACENT channels (a frequent way to share costs with a co-located transmitter, such as Ch18/19 here in San Diego). And of course, moving from UHF to VHF requires an entirely different Antenna and Feedline System.
What happens next will include more use of Hi-VHF and PERHAPS also Lo-VHF channels...although these very long wavelengths are NOT compatible with Mobile/Handheld devices....but they can propagate much further with much lower power, which is reflected by a lower Electric Bill....so should be of interest to stations on a bare-bones budget, e.g. Religious, Foreign Language & other special interest.
Fortunately, MOST Hi-VHF Antennas I've analyzed DO have as much Gain as Rabbit-Ears on Ch2-6, although the SWR is Excessive, which may or may NOT be a problem.
And I've posted several DIY Ch2-6 Antenna designs that can readily fit in an Attic, such as Lo-VHF Folded Dipoles, Lo-VHF Hourglass-Loops and (preferably Outdoor) Lo-VHF Yagis:
[Lo-VHF at Bottom]
Final note re VHF Antennas in Attics....they suffer from several disadvantages compared to OUTDOOR location:
1) Numerous Indoor Loss measurements found that UHF Loss is "typically" 13 dB +/- 7 dB or typical single occupant dwellings (perhaps 10 dB higher for Apts/Condos). UHF is easier than VHF to "leak" in through Windows....but NOT if the Windows are LowE Glass with a metallic coating (20 dB Loss). At VHF Frequencies, Loss through various Building Materials is MUCH LESS...but ACTUAL Loss Measurements are MUCH higher than "predicted". One MSTV Report by du Triel re ATSC-Mobile/Handheld Planning Factors suggested Hi-VHF Loss was 4 dB less than UHF Loss (and Lo-VHF would be even lower):
[Extrapolate "Received Signal Magnitude" Figures)
Although there are many studies of Indoor Loss at UHF Frequencies, there is very little for VHF. Early ATSC Propagation Coverage Tests (1999-2000) included only a couple of Indoor Tests for VHF stations. For WFAA Ch9 in Denver, MEDIAN Indoor Loss of 16.5 dB was found for the 29 Indoor Test Locations. There also was a test on Ch2, but all I could find is fail/success ratio rather than actual signal level measurements.
2) SOME Attics are on the higher end of that scale (or MORE) if an Aluminized Mylar Thermal "Wrap"...or METAL was used in the roof.
3) Your HOUSE contains many potential "Man-Made" Noise sources that primarily affect VHF and esp. Lo-VHF frequencies, which COULD include your LED and Fluorescent Lights, Dimmers, Microwave Ovens
and anything that uses Brush Type (rather than Brushless) Motors, which MAY include Heaters, A/C, Washing/Drying Machines etc. Fortunately, many of these devices contain RFI/EMI Suppression Filters to limit their effect.....and some are miserable sources of interference....