The power bill is the least of your problems in terms of money.
Unless you do class D and/or efficient speakers, you would also need to look at heat management in a rack as well as the associated dust management.
I have just done 21 channels of NAD M27 ncore amps (3). These dont require cooling nor do they have special power requirements. Since there is no major airflow besides passive convection, there is is really not a serious dust issue.
I am still prepping the rest of the setup with a plan for at least a 24 channel atmos/dts prepro to follow. Casablanca V and trinnov look like good frontrunner options. Datasat and theta's implementation are still a bit of an unknown quantity with final costs of dacs etc being unknown.
I would have liked a casablanca concept with only 2.4 channels in the main box as a standard with all the rest of the channels priced into breakout boxes. I find that when you put an arbitrary number of channels into the box, a person may be spending way too much for just a few more breakout channels.
I would bet most theta owners want Exceptional 2.x ch audio at the highest technical levels. After that, the number of folks wanting atmos etc will vary. Especially the total number of channels a person wants to do would vary dramatically as well.
A lot of 2ch lovers feel less comfortable with "compromises" made on their 2ch experience but then don't want a separate room for movies.
I would want the 2channel performance to have the of benefit best-in-class dacs, bass managament, perfect digital volume control. 120db-130db+ signal to noise from input to output would be a high priority. The cpu/software in the main box with upgradeable codecs/room correction would be great. Removable hdmi boards would be good as well.
Then throw all other channels in dac/output breakout boxes that are fed digital/processed signals.
I know the card-box designs are also going to become obsolete as well... Especially to discerning customers like theta would have. A cost effective upgrade path might sway some buyers...
if the 2channel box is nearly standalone, a person may be able to use the multichannel boxes with their next theta purchase. Even if you replaced the whole 2ch box (for newer dacs / hdmi / whatever), at least you could rest assured that you arent going to repay for all your multichannel dacs in another 5 years.
The main box is way more likely to become obsolete for one reason or another due to improvements in 2ch dacs, atmos or dts x, hdmi/8k video etc. Along with new codecs and software, even the primary processor in the main box is likely to become obsolete as well... Which is why we are at casablanca V in the first place.