I read somewhere of an idea to Create an ICO of an ERC20 token on Ethereum called Bitcoin, with 21M supply, is it actually possible ?
of course it is possible. bitcoin is not a trademark belonging to some company which can sue you for abusing its name! so you can abuse it anytime you want but the community is wiser than that. they realize it will be a shitcoin. and it has already happened multiple times because people don't realize that it is not the name, nor the supply that makes bitcoin good. but it is the whole system, being decentralized, having limited supply, being safe, having no issues, being easy to use, ....
will a token have any advantage over bitcoin? the answer is LOL. a token is virtual thing that is relying on another platform to function! if that platform goes down or has bugs (which ETH has lots of them) that token will also be affected and there is nothing you (or the token owner/developer) can do about it! bitcoin is a stand alone currency that relies on nothing else but itself.