For me, the question of volatility is not addressed sufficiently. It is of crucial importance if Bitcoin wants to be successful as a currency and not only as a speculative asset ("digital gold" is only another word for that).
It isn't easy to address that in a decentralized way via "infrastructure". But an intelligent design of incentives is definitively possible, for example providing tools that let people profit from stabilizing the price (e.g. with easy to use "contrarian" trading bots) and new services by payment providers like a
"backing" option for merchants.
The area I think development is needed now is on the issue of synchronisation in the area that, an individual having an account on BTC.com. Blockchain.info, Xapo, Paxful, and other wallet providers but no one can see that or he has to download all of this providers app in other to keep his funds safe.
I don't get what you mean. The wallet services you mention are centralized online wallets, and everyone of them works "on its own", without needing another app, not even for "keep funds safe" like you say. And don't forget that the "ideal situation" would be everybody using real clients like Bitcoin Core or at least Electrum.