The one thing around which the majority agrees is that
BTC ETF will cause significant price increase, and some very often referred to gold as an example. But for me personally this is not a good example, gold is something completely different, and the only thing gold and
BTC have in common is that they can both be store of value.
However recently I read what theymos is write about ETF, and I realized that few people actually wonder what will be a long lasting consequence of ETF. But perhaps it's best to read what our admin thinks about all this and some other important things.
Andreas Antonopolous: ETF's are NOT good for bitcoin as the centralized custodian can decide what to do with the bitcoin they're holding.
Agreed, an ETF will almost certainly turn into a disaster at some point. The coins will be stolen, forks will be handled controversially, there will be issues with fungibility (eg. someone will "trace stolen coins" to the ETF's stash), the world will freak out when a bunch of retirees lose their life savings after doing the equivalent of buying BTC at $20k, etc. etc. It'll also get the sort of people who love regulation more into BTC, which is never good.
But investors want it, so it'll probably happen eventually. In particular, I totally condemn trying to get regulators to interfere in the free market more than they already do by blocking any ETF. (When the SEC was last looking into this, I had actually written a long document that I was going to send to them in order to comment on many technical issues with their proposed Bitcoin ETF regulation, but I decided not to send it because I don't want to have even the slightest hand in regulations.)
An ETF probably will increase the price a lot (until the ETF suffers its near-inevitable catastrophe), which has some pros and cons.
Note that an ETF can't affect Bitcoin itself, just the ETF investors and the market. There is no voting of any sort in Bitcoin, so it's not as if holding a lot of BTC gives you any power over Bitcoin, for example. I do agree with Andreas that the creation of a "corpo-Bitcoin" seems probable, perhaps after the ETF loses a ton of BTC and wants to undo it.
Thanks to bitmover who post this and some other good post from theymos reddit account :
https://bitcointalksearch.org/topic/theymos-activity-on-reddit-a-collection-of-posts-5153962