I think there is some question about the leaking of keys from BIP 157 filters. Easiest remedy is running your own full node and connecting to it, less effective would be using tor to connect to a BIP157 node. Best is running your own node(s) over tor and connecting your light nodes to it.

I think it's really not that long before such hardware is practical for such a purpose though. We have a little ARM64 board here, probably half the size of a rPi, we intend to develop something like this as a BTC/LN/Indra relay turnkey device. The problem with the mobiles is simply power and disk at the same time, they don't have eMMC SD cards commonly anymore, and OTG cables for USB-C don't seem to come in a charge-and-connect variety, when the socket is in host mode with a device plugged in it doesn't allow the charging at the same time. At least I haven't seen one. That's the only thing that is needed. I have a 1tb SSD I could use right now if this was possible, but without having power at the same time it's impossible.