@oblomov 
One thing at a time.
I'm interested into feasibility, I tried to compile both snac2 and gts with some issues, so i want to see if someone did it, even on a rooted one.
But anyway
- you can use a higher >1024 port so no need for root
- a dyndns client for android, with a free dyndns account
my main instance can change ip or go down for hours, though way less frequently than a mobile phone on mobile data.
a dyndns client will point lucaphone.dyndns.org to my mobile ip:8443 with a quick ttl (matter of 5 minutes time)
all other fediverse servers keep trying for days to sent stuff to lucaphone.dynsdns.org until they resolve the current ip / a running server / with proper keys