So, my experience ...
Using the migrate function of NSRU actually worked quite well, even between FW instances 2 yrs apart. In total I had about a half-dozen issues to be resolved, and found an additional 3 problems in the NSRU tool itself. I will post a separate note with those details so it's not lost here.
I did have an issue with dnsmasq, but it wasn't the concern you raised above with dhcp_staticlist. Even though NSRU loaded the "old format" dhcp_staticlist from 380, upon boot, the new FW automagically converted to the two new dhcp_staticlist and dhcp_hostnames so all of my previous reserved IPs transferred fine. My issue was with a custom 'dnsmasq.conf.add' where I set some non-expiring (i.e. infinite) leases. The technique that worked in 380 and earlier caused dnsmasq to exit and restart (rolling), but I figured out an easy fix that involved moving that customization to a 'dnsmasq.postconf' that now works under 384.17.
My other major issue was with openvpn server and related firewall customization associated with the changes made in 384 around the "Client will use VPN to access" settings. I like the new settings and logic, but it broke my old config. In the end it was a fairly simple fix, but I had to get my head back into iptables and openvpn config files, which, when you don't deal with it for a while gets really murky (at least for me).
All in all, a fairly good experience with NSRU as a restore tool. The vast majority of my system transferred in and just worked. I'm still glad I had the spare router to test on as it greatly reduced my network down time. I was able to swap in the new router (with the new FW and migrated-in settings) and observe the issues, then swap back to the old (380) and have a working network while I researched and fixed the problems. A couple of those cycles over a few days in my spare time and it all came together well.
Thanks for your (and your predecessors) work on this great tool.