AFAIK bitcoin was created as a p2p cash in the first place and i hope in the future it gets closer to this purpose, and i think it can get there too if the number of users increase and the volatility decreases.
That's a rather complex problem (volatility) that is not directly related to the debate. Bitcoin should be able to always accommodate new users; as long as it continues functioning the same way that it does. The problem that we can run into is that suddenly 1 million people (arbitrary number) want to buy Bitcoin and create 1 TX in a day. This would create a 'heavy' backlog because the system is only able to handle 3 TPS at the moment. This is why we need everything (to be ready and prepared):
1) Segwit
2) Block size increase
3) Lightning Network
4) Sidechains
The network should not have backlogs unless it is under attack, else I don't see how it could be considered 'P2P cash'.