No need to know how many coins have been lost.. What's the point ? Why you think it's important to know about how many coins are lost/remaining ?
Every market thrives on information. I would argue that large uncertainty about the amount of lost coins is hurting bitcoin adoption, especially its use as a store of value. I think this proposal would help bitcoin adoption by providing a count of the number of controllable coins, and it would do so in a manner that would not unfairly penalize anyone.
People who understand Bitcoin well enough to be uncertain about the lost coin situation aren't the type of people who are on the fence about adoption. Go ask 1000 people who haven't started using Bitcoin yet, and I bet no one will tell you that their sticking point is the lost coin issue. Either they won't know anything about Bitcoin, or they'll say "it's not backed by anything", "isn't that a pyramid scheme?", etc.
Restatement of the problem: Assume in the future lots of people hold a lot of their wealth in Bitcoin. Some previously inactive huge store of bitcoin comes onto the market, and the price of BTC falls 5%, hence the value of everyone's bitcoin holdings fall by 5%.
A couple reasons why this isn't a huge problem:
-Once bitcoin is mature, people will no longer need to hold large amounts of it for speculation purposes, the same way that wealthy people today don't generally hold huge amounts of cash. Anyone who has invested their wealth in stocks would be relatively protected. Bond contracts can be written so that payouts are inflation adjusted.
-If people are really concerned about this, companies will offer 'inflation insurance', removing your uncertainty about your own bitcoins value if new bitcoins come into the market. The price of this inflation insurance will reveal what the market thinks about this risk.
-As long as bitcoin is in its growth mode (i.e. until it takes over as the default world currency), any reduction in BTC value caused by coins that were assumed to be lost coming into the market will likely be negligible compared to forces stemming from speculation about Bitcoin's eventual level of success.