I've looked at income statements of a bunch of public companies that mine Bitcoin, and one of the most striking things is how much of the cost is actually depreciation of hardware. Granted, part of this is that they are running the hardware to its limits, but another aspect is that new improved mining hardware comes out frequently and pushes the old hardware over the profitability edge.
Basically, I'm skeptical that anyone can mine Bitcoin profitably without running the hardware 24/7. Other coins that use commodity hardware, maybe.
May well be that it won't change the cost structure enough - I treat this as the president deciding an announcement like this, which amounts to little more than "I've asked them to look into it", as a way to get some publicity. It could very well end up being silently put aside if the costs don't stack up.
This idea was presented to President Bukele during a Twitter Spaces[1] session where he discussed the bill with the Bitcoin community whilst it was going through voting. Mining Bitcoin was not something he has previously considered and openly ideated on the call with the community. It seems like a fully proposed plan for how Bitcoin mining will play a part in the country's overall energy policy has likely not yet been fully formed.
But the potential geothermal output for El Salvador is huge.