In fact the technical problems are so severe that it's questionable if the switchover will happen at all. All current PoS coins use centralized control due to these technical issues.
NVIDIA GPUs are actually typically more efficient for mining most coins, AMD cards are only preferred because they have quicker ROI. If mining profits continue to decline, that efficiency comes more into play. And, NVIDIA may be about to introduce a new generation which further improves efficiency.
If they do, god only knows what the prices are going to be. They're already nuts on Pascal, let alone if miners are snapping them up for the efficiency. Availability is going to be shit too.
In what way are nvidia cards more efficient? Vegas are in some cases much faster and at worst equal to gtx 1080.
The usual way, i.e. "efficiency=performance/power"? Here, I did the math for you. Numbers from whattomine.com:
https://i.imgur.com/2u2HOw7.png
https://filebin.net/fr1sqfwtvulkoynu/gpu_efficiency.ods
As you can see, apart from Vega being a very efficient Cryptonight miner, and Polaris being an acceptably efficient Ethash (Ethereum) miner, AMD cards have absolutely garbage efficiency, they use just tons of power for their performance. And they are one-trick ponies: there are only one or two decent algos for AMD cards.
The 1080 and 1080 Ti specifically have problems with a few algos due to their GDDR5X (which results in half of the memory bandwidth being wasted) but on the whole NVIDIA cards are extremely efficient miners across a variety of algorithms, and usually keep up with AMD on efficiency even on Ethash.
The 1070 Ti, in particular, is the reigning champion of efficiency. It's basically a 1080 with GDDR5 instead of 5X, which makes it the most efficient card in most algos, and its worst-case is "only" being as efficient as a 580 at Ethash.
Again: people prefer AMD cards because they ROI quicker during the booms. The half of this that efficiency obscures is power: AMD cards have higher TDPs and are capable of pumping out a lot more watts per dollar (RIP Planet Earth). But when profits are down and efficiency matters (or for those with expensive electricity), NVIDIA is better, and you also have that flexibility to move across algorithms if there is a hot new currency.
There is also a pretty substantial cargo-cult with regards to mining: people use AMD because that's what they see other people using, and they don't bother to do the math. But NVIDIA has the same efficiency advantage in compute as they do in gaming: 1.5-2x the performance-per-watt in most situations.
https://www.techpowerup.com/reviews/Sapphire/RX_580_Nitro_Pl...
https://www.reddit.com/r/EtherMining/comments/674evm/rx_580_...
Again: AMD is way, way behind on efficiency and has been since Maxwell. There are a few algos they do well on, but on the whole they are roughly a generation to a generation-and-a-half behind NVIDIA (Vega 56 is roughly as fast and efficient as a 980 Ti). You buy them because they're cheap for the hashrate, not because they're efficient. Think cheap-and-nasty here.
The thing with AMD power measurements that you have to be real careful of is that AMD's sensor is only reading the core power, not any power spent on memory or any losses in the VRMs, and they do it very inaccurately (and don't account for efficiency/etc). So you should be taking people's chatter on Reddit with a big grain of salt - unless you are measuring the power at the wall, or using a digital PSU, you are probably getting figures that are ~40W low, and potentially have 20% variation or so from the actual figure. Anyone using GPU-Z to measure their card is doing it wrong.
Right now that makes things hard for everyone not a miner, but if AMD ends up being the only option for gamers while Nvidia still sells to miners, they might actually gain from the mess.
I actually think AMD's timing on increasing production is really questionable here. Barring another major runup in Bitcoin prices (altcoin profitability follows Bitcoin prices), which seems unlikely at the moment, network difficulty will continue to increase and mining profits are going to continue to decline. That means miners are going to taper off purchases, and some may even be dumping their rigs.
So AMD is essentially increasing production at the exact moment when they may already have a problem with the market being flooded. The time when they needed to increase production was 4 months ago, it's too late now.
On top of that, NVIDIA may be pushing out their new GPUs within the next few months, implying another step in efficiency which puts AMD's performance/efficiency even further behind. They are already about a generation behind (roughly competitive with Maxwell), despite being on similar nodes. I'd be prepared for NVIDIA to make a minimum of a half-gen step (30%), if not a full-gen step (60%).
AMD's timing seems exquisitely poor here. They didn't want to bet on crypto, and now it's too late. Fortune favors the bold.
Offtopic FYI: GPUs that are in use 24/7 would probably in a better shape than those that encounter more thermal (on/off) cycles. There's obviously more wear and tear on the moving part, but fans are easier to replace than mechanically stressed silicon/PCBs.
b) have you actually tried replacing monstrous coolers on moderns cards? Or even buying spares? It is rare, expensive, hard to disassemble and hard to fit back. Some cards even use glue stickers on memory thermo-interface, you can potentially tore chips away.
However, there are tons of threads due to skyrocketing memory and GPU prices stating that it doesn't make sense to build right now and you can get better deals on pre-built machines.