Source: someone who just declared Dropbox critical despite having invested an ungodly amount of time into first an old PC with ubuntu and nextcloud and now my NAS box which I love dearly but is a complete dumpster fire even though I'm tech-literate enough to engage with the enormous number of low-level decisions it regularly throws at me.
It gets new security vulnerabilities every damn week so you can't just turn on the public-facing web services. If you still want those -- and if you want it to replace cloud services, you do -- you'll need to configure the VPN, which is an enormous hassle on both client and server. Also, sometimes there's an update and it just stops working until you pay attention to it. Ditto for network shares, but I think the problem there is in Android / iOS network filesystem implementations. It often Just Doesn't Work, and then I try dropbox and it Just Works. Even when the NAS network share does work, managing permissions is a nightmare, even for simple setups, ditto storage, ditto the VM that theoretically runs nextcloud but in practice gets taken down by an update on a regular basis.
For my next NAS I'm going to try Synology, but they depend on many of the same open source projects that I've seen Just Not Working on the QNAP side, so I'm not terribly hopeful.
Nextcloud devices look promising in the long run but the market hasn't shaken out yet so you're either going to have to invest tons of time in research or you're going to have to do trial and error. In both cases you'll have to make up for deficiencies.
What would be the difficulty with a vpn? Synology has VPN on device. It seems to be a matter of enabling it. Routers also typically include vpn functionality.
So no, it's not easy, it's a lightweight IT gig just to connect to your damn server! This is one of those tasks that I regularly see highly capable techies underestimate because of some combination of getting lucky on a small number of deployments and/or their brain engaging in protective amnesia to protect them from living with the scars of having wasted big chunks of otherwise perfectly good life fiddling with VPN settings.
Being able to serve resources on the open internet is extremely important and NASes clearly aren't up to the task yet.
https://pando.com/2012/02/26/steve-jobs-was-right-dropbox-is...
I believe Steve already saw the fully realized platform of cross device computing in 2001. iPod illuminated the idea that context can birth new device classes, so naturally if you're going to have the same person use multiple devices, their context should morph to the device while being consistent in a global user state. This means that a file syncing (and by extension file sharing) feature is absolutely required to be fluid and desirable as a consumer product.
Firewire was created in part because of this desire for the file sharing to be seamless - now Dropbox had a real-world tested wireless and continuous implementation running on Apple hardware, of course it's an acquisition target (I'm just surprised he didn't go higher knowing how much trouble MobileMe / iCloud accounts were at the time).