Read an article once, author claimed up to 30% coins are lost forever.

I think it would be hard to find amount.   You might be able to find BTC adress with no activity, but part I don't see is how you could tell cold storage holding (with no one depositing more) compared to a lost account.

I do think it is not something that will repeat its self.   I would guess most lost were CPU and GPU days.  But that is just my feeling as price was lot lower then.

There's no way to tell but it doesn't really matter how many are in circulation but 21 mill is the number that will be mined. I don't think just because they haven't moved means they are lost though as some people will just keep them safe and hold for the long run (though also some coins will naturally be lost or forgotten about too).

Well I think that is logical, but it doesn't mean they're all lost. My first coins haven't moved in years since I bought them and likely won't for a very long time and if you see the potential in bitcoin I think others will feel the same. If satoshi is alive I can't see him just abandoning his coins forever either or would like to think he still has access to them at least.

Nothing. It would just make the remaining coins even more valuable. More decimal places could be added too if coins were so scarce so smaller denominations weren't worth ridiculous amounts.

it would make sense for people who bought btc in 2011 and 2012 to at least sell a few coins at $1100 peak.
maybe they just can't access their wallet or they will leave them untouched for like another 10 more years.

Anyone can claim any amount of coins have been lost; absent coins being burned to a verifiable burn address, there's no way to prove any loss.

Yes, if someone comes along saying they lost 5 BTC, I will fee horrible for them, but even if the sum of coins reported lost by people to things like crashed hard drives, etc was 2 million, in my mind, I wouldn't think that the remaining coins should be any more valuable, because there is no way to prove those coins lost, rather than people trying to manipulate perceived prices.

People come up with all sorts of theories about when to say that coins have been lost; if they haven't moved for X amount of time, presumed lost, etc... That doesn't make sense.

First off, early miners could have simply backed up their wallets and haven't felt the need to combine all of their coins at a new address, and a lot of people claim to have created paper wallets and done things like burying them somewhere. Those coins won't move either. Really, just because a coin hasn't moved from its address for a while, that's no reason to assume its lost. Or, at the least, it would be very unwise for people to try to adjust value of the remaining coins, as those coins "lost" could move at any time. There's no proof the private keys for older coins have been lost, in many cases, no ones even claiming the key has beeen lost, it's just that someone is speculating that the key is lost due to the lack of movement.

30% seems to be too much.

That means on average everyone who owns 1 BTC would likely to lose 0.3 BTC lol.  

Is there concrete proof that nobody can access those coins?

This is what I mentioned earlier.  It is just hard to tell the difference between the two as they appear the same.

I do think there i a high chance lots of CPU coins did get "lost" in one way or another.  But it will always be a estimate no way you can tell for sure.