I just went through the same upgrade (my SG-1000 was a rock for the ~7 years I had it in use) and found this thread very helpful. After a few attempts, I was able to get a working xml that imported everything correctly into the SG-1100.
I had a bunch of vlans with opt interfaces that needed to be re-mapped into the internal switch. I started by booting the SG-1100 and exporting the default config to look at side-by-side with my SG-1000 config.
I decided to keep my interface mappings of <opt#> to vlan consistent, so I re-mapped the builtin OPT port on the SG-1100 (<if>mvneta0.4092</if>) to <opt0> in my xml file. Since the SG-1000 doesn't have this port, my initial conversion process left it unused
In the <interfaces> and <vlan> sections, I merged the SG-1100 defaults with my custom interfaces/vlans
for the custom interfaces, I changed all the <if> tags from cpsw* to mvneta* but kept the subinterface numbers the same
for the vlans, I updated the interface names to match what the resulting data interface data
I also had to copy the <switches> section out of the default SG-1100 export and populate the <vlangroups> and <swports> subsections with the proper port tags / pvids for my vlans
Just sharing my notes in case anyone else is searching for help with the same upgrade.