Any blockcahin is capable of recording Proof of Existence. There are open source scripts that can be modified to the coin of your choosing.

Set up a server (AWS, etc.) and install:

https://github.com/iquidus/explorer

Then point your sub-domain to the server running Iquidus.

There are other open-source block explorers but Iquidus is popular and easy to set up and customize.

If there are no nodes a coin is dead. Even if it can be traded, without nodes the coins can't leave the exchange so they are no longer a coin, just orders on an exchange.

Very interesting.

Hopefully we will see more of this in the future.

An interesting read:

Scams or Not, Crypto Tokens Have History on Their Side
http://www.coindesk.com/scams-not-crypto-tokens-history-side/

Margin trading for coins can help increase their volume and liquidity which can be very good.

There are still many challenges facing crypto and there will be many coins that help move everything forward.

For a coin to be successful it needs people who use it.

Curious to see how this develops.

What is considered "widely"?

One word: Many

And lots of them probably won't come from the present top 100.

Pretty sure a Delorian is helpful for this. I've seen movies (I think they were documentary) where there was mixed success.