Usability I think it is.
Consensus is what makes a currency working, but how people reach consensus if they even can not understand it ? When you said Grin is a better digital currency because of privacy, scalability, blablabla, I said “it sounds good, let my try it” , and failed on sending the hello-world money to my friend with any of the wallets, just because her wallet is not online. Then you said she just need to run a local grin wallet and node on her linux server. but she even doesn’t know linux at all. We can’t expect the currency users including miners are all tech guru, or their amount is not big enough to support a currency.
So making Grin easy to use is the key to make Grin grow fast enough to avoid death, including some kind of asynchronous transferring, easy-to-use wallet and mining tool which I’m working on. Hopefully more developers of Grin will go on this way.