Lost/forgotten/locked Bitcoins There are currently ~16 million bitcoins in circulation at this moment. There will only ever be 21 million coins. What about all the coins that have been locked in wallets due to loss of keys, owners of wallets dying, etc...?

The number of lost coins is probably fairly small now but if Bitcoin is going to be relevant for who knows 100, 200 or 300+ years, this number will increase. I guess the reduction of "usable" coins will increase the price per coin and the majority of coins won't ever be lost so this not a significant issue. 

Are there any solutions to lost coins or is this just a feature of the decentralized network?
What about all the coins that have been locked in wallets due to loss of keys, owners of wallets dying, etc...? 

There is no way someone can tell you the exact amount of "locked" bitcoins. Even after looking into blockchain and building the system of how often bitcoins move from one wallet to another. There are many people who have bitcoins and sitting on them for many years, but still have the access and can use them anytime they want (it can be considered as lost bitcoins, but it's not). So it will be impossible to track how many bitcoins are lost "forever" by users.

Are there any solutions to lost coins or is this just a feature of the decentralized network? 

There is no current solution and I'm not sure there will be one. Bitcoin wallets/storage services improve their security and adding more and more features to recover your keys, passwords, etc., but it has nothing to do with those people who lost it long time ago.