Haviong trouble finding it now, but google "lightning network routing problems" and you'll get a lot of results. IIRC the fundamental issue boils down to a hard mathematical problem about node traversal that is not yet solved. I am having trouble recalling the name right now, apologies.
> AFAIK if you're not a payment hub (ie. you want to route other people's payments) you don't need to be always online.
There have been ways that a counterparty can close a channel in their favour if you aren't online. Perhaps this has been fixed by now.
AFAIK the fix is to have a service (or multiple) stay online for you, and I believe it could be done without requiring access to your private keys. If your counterparty broadcasts a stale transaction that's in their favor, your service will broadcast a newer transaction that reverts it.
can you elaborate on this?
>a need for always-on nodes
AFAIK if you're not a payment hub (ie. you want to route other people's payments) you don't need to be always online.