Speaking as a Sia developer, I can address your concerns.
> these networks don't impose any minimums for the upstream bandwidth of the hosts.
Sia today primarily handles that through gross redundancy. If you are using the default installation, you're going to be putting your files on 50 hosts. A typical host selection is going to include at least a few sitting on large pipes. Downloads on Sia today typically run at about 80mbps. (the graph is really spiky though, it'll spike between about 40mbps and 300mbps).
We have updates in the pipeline that will allow you to speedtest hosts before signing up with them, and will allow you to continually monitor their performance over time. If they cease to be fast enough for your specific needs, you'll drop them in favor of a new host. ETA on that is probably ~August.
> Files can completely disappear from the network if the machines that are hosting them happen to go dark for whatever reason
We take host quality very seriously, and it's one of the reasons that our network has 300 hosts while our competitors are reporting something like 20,000 hosts. To be a host on Sia, you have to put up your own money as collateral. You have to go through this long setup process, and there are several features that renters will check for to make sure that you are maintaining your host well and being serious about hosting. Someone who just sets Sia up out of their house and then doesn't maintain it is going to have a very poor score and isn't going to be selected as a host for the most part.
Every time someone puts data on your machine, you have to put up some of your own money as collateral. If you go dark, that money is forfeit. This scares away a lot of hosts, but that's absolutely fine with us. If you aren't that serious about hosting we don't want you on our network.
> but lack of clarity around some important concerns have so far prevented me from taking them seriously
We are in the middle of a re-branding that we hope introduces more clarity around this type of stuff as it relates to our network.
> these networks don't impose any minimums for the upstream bandwidth of the hosts.
Sia today primarily handles that through gross redundancy. If you are using the default installation, you're going to be putting your files on 50 hosts. A typical host selection is going to include at least a few sitting on large pipes. Downloads on Sia today typically run at about 80mbps. (the graph is really spiky though, it'll spike between about 40mbps and 300mbps).
We have updates in the pipeline that will allow you to speedtest hosts before signing up with them, and will allow you to continually monitor their performance over time. If they cease to be fast enough for your specific needs, you'll drop them in favor of a new host. ETA on that is probably ~August.
> Files can completely disappear from the network if the machines that are hosting them happen to go dark for whatever reason
We take host quality very seriously, and it's one of the reasons that our network has 300 hosts while our competitors are reporting something like 20,000 hosts. To be a host on Sia, you have to put up your own money as collateral. You have to go through this long setup process, and there are several features that renters will check for to make sure that you are maintaining your host well and being serious about hosting. Someone who just sets Sia up out of their house and then doesn't maintain it is going to have a very poor score and isn't going to be selected as a host for the most part.
Every time someone puts data on your machine, you have to put up some of your own money as collateral. If you go dark, that money is forfeit. This scares away a lot of hosts, but that's absolutely fine with us. If you aren't that serious about hosting we don't want you on our network.
> but lack of clarity around some important concerns have so far prevented me from taking them seriously
We are in the middle of a re-branding that we hope introduces more clarity around this type of stuff as it relates to our network.