It will. Via second and third layers. It'll scale just fine. An example second layer that you can use right now is the lightning network https://lightning.network/
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.
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.