I've make few tests and appear to work.
Few considerations:
1. java3d 1.7.0 (last stable) in place of 1.6.1.
-I knew it's a lot of work and I'm available to help
2. If java >9 don't like last java3d You could keep java 1.8
3. About Windows XP and 32b linux could be useful an opinion pull to see who still need it.
4. About java: almost all OS have their own politics and usually don't fully work with SH3D. So to bundle proper java in the same package I think is the best solution.
5. About polyline:
5.1- I like to modify individual segments (straight or curve). Could be more simple to make furniture icons like in CAD programs.
5.2- Add name for polyline.
6. About text (all texts): I wish to have for all the same options like are already for labels (furniture & rooms name, dimensions etc.).

Anyway You've make a great job all the time.
Many Thanks and stay healthy [=D>] .