On the scalability issues of onboarding millions of LN mobile clients

The discussion revolves around the idea of private full nodes serving headers to a handful of weak devices as a solution to various problems in a future full of LN + SPV nodes. The main challenge is making the UX of connecting a mobile LN client to a home full node easy enough so that centralised services can't improve much on that step. Start9 Labs is researching this area, and they've found that the main UX challenges are around installation and configuration of server applications, as well as educating users on the distinction between client and server apps. Apps that either require "zero configuration" or have very easy in-app walkthroughs of the bare essentials of configuration and GUI style installs of server applications familiar to those who have installed desktop or mobile software could help solve some of these issues. Once a full node has synced the whole blockchain and the total set of headers is known, one doesn't actually need to carry 100% of the block data, as they can re-fetch a needed block from elsewhere and verify the block data matches the header they've already checked for consensus. From there, the header chain can serve as base truth for a whole set of L2+ services or L1 SPV wallets. The issue isn't that Lightning does SPV, but whether or not the node it is tethered to is actually trusted since SPV necessarily trusts some dimensions of the information supplied to it. Doing SPV against a full node you own is no more dangerous than indexing watch-only addresses in Core and then asking for wallet/utxo information over RPC.