Newer cryptocurrencies have more sophisticated governance structures than Bitcoin (see: Tezos). Some of them could allow for an elastic monetary supply. The downside of these systems is that it takes a lot of work to properly encode the specific set of rules which decide when to increase the supply, and how to distribute the new supply. The upside is that these rules actually exist and are unambiguous.
It's appealing because it keeps politicians honest, but if you have honest politicians it is just a thought experiment.
I think a constrained monetary supply just means the politicians we elect have less influence over the economy than the people with the most wealth. In either scenario, there will be untrustworthy politicians who need to be out voted or voted out.
The last 60 years on a macro level have largely proved the Keynesian model. I think we're right to put faith in politicians in general. The solution might just be holding currency from another nation instead of your own.
Fixed monetary supply might be one thing in theory, but fixed credit supply is the death knell to an economy. And the two are usually complimentary. Monetary supply can fill in the potholes of weakening credit supply when the latter contracts - and it inevitably will when the private issuers that generate those debt contracts pull back in a recession. If you have your hands tied to some constrained supply like gold or bitcoin, like what happened to the central banks after World War I and into the Great Depression, you end up backed up against a wall.
That said there is certainly something that's personally appealing about an asset that's guaranteed to maintain the supply side of the equilibrium. As an investor you only have to consider demand. But for any kind of widely used currency that backs an economy it's going to be problematic.