I'm not sure if you would run into the problem of availability of hardware at some point, but if you're spending ~$76 billion to rent servers for a day, I'm sure you can figure out the details later.
Someone ran the calculations (From Aug 1st of 2017) here: https://freedomnode.com/blog/86/cost-of-51-attack-and-securi...
But logically, 51% of the network cannot exceed the value of the network. You lose by a huge margin if you are spending more on protecting your money, than money you actually have.
If the point of the 51% attack is profit-oriented, then the attacker is going to do it long enough to get their double-spend confirmed and then stop doing the 51% attack.
The cryptocurrencies listed in that article are doing pretty well for themselves mining-wise. I suspect that there may be tiny cryptocurrencies traded on some exchanges that could be 51%-attacked by an individual for somewhere between $1,000 and $100,000 to double-spend some high-value transactions. Maybe it's unlikely for the numbers to line up to be profitable and sure enough to pull off, but if it does happen, then that cryptocurrency is toast as soon as someone notices.
If Bitcoin or a top-10 cryptocurrency got 51% attacked, I'm sure the price would take a hit but people would find a way to limit the damage. I'm mainly talking about tiny pump-and-dump-tier cryptocurrencies whose creators don't even love them any more but that inexplicably still have some trading volume.
Relatively short list of "verified" (by a "team of analysts") crypto assets  (YMMV).
Anyone can cook up a coin by forking Bitcoin or Litecoin and do a search-and-replace on the name in the code and nothing else.
Reminds me of how people created a plethora of new browsers on Windows systems by calling a Windows library function that creates a browser. If you didn't know better, you might think that they spent a million man-hours writing a new browser from scratch.
That many ICOs are Ponzi or close to scam is nothing new.Such a list feels more like a personal justification for 'I don't need to invest, I won't miss anything and BTC and ETH were the last success stories in crypto'.
Jest aside, I think there is huge resentment towards cryptocurrencies. From people who missed it, to those who lost. The whole scene is riddled with scams and thieves, and yet it continues to skyrocket. I don't know how this resentment will be overcome, or even if it will be an obstacle to cryptocurrencies, but the resentment is something I've noticed rising at the speed of Bitcoin.
Minkiz has the data ... https://minkiz.co/coin/name/ (basically just a rendering of the metadata in DOACC (https://github.com/DOACC/individuals).
Admittedly I stopped recording in March last year but nevertheless.