I'm not entirely sure what you are asking here - I think you might have your terminology wrong.
I might, but what I want to say is that even if we make all those assumptions you wrote, it's still impractical to open a channel for every future Bitcoin user. We'll probably have to move into another smarter way like using 1 multi-sig address for a family; each member could have their own balance in their phone, but they'd all spend from the same channel.
Sure, you can! I have recently opened two channels in a single transaction. As far as I know, LND, which seems to be the most popular implementation, requires the operator to construct such a transaction manually using PSBTs. That's probably why it's not so popular. C-lightning has a dedicated
multifundchannel command which is fairly easy to use. I don't recall seeing a mobile wallet which would support this feature.
There's a lot of development in LN these days as I can see. I'll dive into the details this summer, because I've stayed behind. I have never setup a lightning node like LND and C-lightning; I'll start with these.