I still can't figure out why this never gets more traction. The size of the House was routinely increased after the census every 10 years, up to and including 1910, when it was increased to the current 435. After the 1920 census, the size was not increased, and then a law was passed in 1929 that permanently set the size at 435. Guess which party controlled both houses and the Presidency in the 1920s?? Yep, you guessed it!
One of the reasons given at that time was that cities were filling up with (European) immigrants, and more House seats from those populous areas would dilute the political power of "real Americans." Gee, doesn't that sound familiar??
But think about that - after the 1910 census, the population of the US was one-third of what it is now. New Mexico, Arizona, Alaska, and Hawaii weren't states then. Women had not won the universal right to vote at that time, and most African Americans and Native Americans were disenfranchised as well.
The size definitely needs to be increased to at least account for those new states, and to also grant DC a full-fledged voting member of the House. And the BIG thing, though - the size of the House determines the number of electoral votes that we have in the Presidential election.
If Dems retake both Houses and do away with the filibuster, this could be done. It's completely Constitutional, as far as I can see.