I currently use Leste on my N900 where it barely works. The hardware is very ancient by moderns standards and the basic kernel+services+X11 already swallows most of the 256MB ram.
The Droid 4 has 4 times as much CPU power and 4 times as much RAM and a slightly faster µSD interface. The system should be blazing fast on there. I just freed mine from old data and will try Leste in the next days. Will report back to you :)
Of course you will likely need a modern mobile phone as hotspot because 3G is shut down in most countries and 2G speeds are something else.
I think you can also expect a blog post from the Leste folks in the next week or so about their progress in the last year. E.g. the migration to Devuan Excalibur (~Debian Trixie). I am constantly astonished what the small group manages to do, as I am with @TheMightyCat and his progress on the Fairphone.