Could easily be 25%. T-Mobile as part of the Sprint deal committed to selling fixed wireless to 8% of the US. It has guaranteed that 90% of Americans will see mobile broadband service at speeds of at least 100Mbps if the deal is approved.
Goldman Sachs estimates Verizon will sell fixed to about 8% of Americans by then. That's ambitious. It's based on Verizon selling 25% of the market from cable in the ~30M homes Verizon will pass. Most are in the 70% of the US where Verizon has no good landline offering. It is pricing aggressively at $50-70, well under cable's price and offering much higher upstream. Verizon is still moving full speed ahead on mmWave, although Consumer CEO Ronan Dunne recently confirmed many consumers in other locations will be connected at lower speeds in mid and low-band spectrum.
CEO Randall Stephenson of AT&T, who will have a great deal of mmWave capacity to sell in 2021, has specifically said he will have a fixed offering. AT&T does not have landlines in over 60% of the US so will almost definitely sell fixed wireless. It has released no numbers yet, but certainly has plans well into the millions.
If T-Mobile-Sprint goes through, Dish is committed to covering 70% of the US by 2023. The primary product will be fixed wireless and Charlie Ergen is betting $10B he will sell a lot of it. He certainly will sell enough to push up this estimate.
If the merger doesn't go through, Sprint will have a massive amount of unsold capacity from the 160 MHz at 2.5 GHz it is lighting across the country. They would be foolish not to sell fixed aggressively. Masa-san is not a fool.
Starry has raised $100M. C Spire, with 1 million mobile customers, is aggressively selling its version of fixed. Small wireless ISPs have over 1 million connections.
I consider anything 4-5 years out a guess, but in this case it is well informed.