So, in areas where a provider only offers 20 or 50... will they just stop serving that area until it's financially worthwhile to upgrade that equipment?
No. The minimums set by the FCC are just the minimums for the service to count as broadband. There's no requirement that a given internet service actually is broadband internet service. The worst that would happen to the provider is that they might not be eligible for some government programs that promote broadband.
The law requires the FCC to regularly check on the availability of broadband in the US and to determine if it is being deployed in a reasonable and timely fashion. If they determine it is not they are required to take action to accelerate deployment by doing such things as removing barriers to infrastructure investments and promoting competition.
