Effective like prohibition was? Or the war on drugs? All that will happen is people will stop using macOS and Windows because that is all the US government can pressure.
The effectiveness of limiting proliferation is tied directly to the difficulty and the scarcity of the human capital involved, this is why restricting the proliferation of small arms which can be build by anyone with some machining experience is near impossible, but limiting the proliferation of say nuclear arms and technology is quite possible.
It would surprise me if the NSA (or any other agency) doesn't have a list of all or most software engineers and mathematicians which are capable of designing crypto, that mailing list isn't that big.
People can easily hide data streams inside video-streams/ text-files/images to circumvent trivial screening. The government won't be able to do anything effective without massive costs and draconian measures. Not to mention people outside the US can carry on however they like anyway.
What will happen if say we do wake up to a post quantum world with much of our asymmetric cryptography being worthless. Do you really see people being able to develop a new RSA level family of algorithms at a hackaton?
If you can't increase the work that needed to be done to break your encryption at the same rate as your adversary increases their capabilities you are going to lose and lose badly.
And draconian measures and extreme costs is just what they are proposing, I'm not advocating that it's going to be effective at first or cheap, but dismissing it as even if they want too they will never be able too is just as foolish as voting for Trump ironically to give him a sympathy vote.
Go ask people from East Germany, pre-Glasnost Russia and even some countries that exist today how easy it is going to be to evade surveillance enmass.
You should never be dismissive of threats no matter how far fetched or unlikely they are or how incapable your opponent at executing them might be, this is probably one of the more important lessons one can take from history.
The threat you describe sounds like a race. But in fact, it's more like a switch. Right now the world is pre-quantum. When the switch is flipped, to post-quantum, a lot of algorithms will break. But not all of them.
See http://pqcrypto.org/ for some interesting reading.
Post-Quantum Cryptography, Bernstein, 2009: http://www.e-reading.club/bookreader.php/135832/Post_Quantum...
Regarding your point, I don't think that people here are being dismissive of your ideas. You're quite right. But there are reasons to be positive about the future, while highlighting the negatives. Isn't it so interesting that certain algorithms can be safe in a pqcrypto world?
Notice where the algorithms spring up from. You mention a hackathon, but that's not where these algorithms root. They're from universities. And universities are interesting. If the legislation will face resistance, it will probably be from academics, like in the last crypto war.
How easy would it to work on open encryption software if we'll have to revert to the Pre Bernstein V. United States era (which wasn't so long ago) and one that might actually be more heavily regulated than (restriction on actual work on encryption and related field rather than exporting software) before? Heck Phil Zimmermann almost ended up going to jail when PGP was "leaked" outside of the US, and this isn't East Germany, this is the US in the mid 90's.
This thread's article is interesting, because it's the first step toward a world you describe. But reason has a way of prevailing. Not always, but usually.
One thing that's missing now, that someone here might want to cook up, is a good explanation. The topic of crypto is difficult. Not just because it's hard like calculus, but because there are a lot of subtleties. Old analogies to locks and doors aren't really applicable. What we need is a way of highlighting what's going on, why people should care, and what they can do.