Sometimes I go into my "experimental-mode" and just get an itch to try something differently. There no real reason to cut that "Mother" 'Celadine' off, other than to see what happens.
All my plumeria are potted but some of the larger ones have their pots in the ground, just so I don't have to water so frequently. I never let any of mine get over 5' though. That's because they all have to come in for their five-month dormancy and they are stored without light, soil, or moisture in large contractor bags. I take cuttings to control their height/width. Since I have my (tiny) tropical plant business, I sell those cuttings.
I have taken pictures of my three, 25+ year old "Mother" plants and a rooted cutting. The first pictures are of the 'Celadine', the second pictures are of the 'Scott Pratt', the third pictures are of the 'Vera Cruz Rose'. The final picture is of one of the rooted cuttings of the mother 'Celadine', and that's probably now a 10 year old plant. The can is a standard, 16 oz. size. You will see all the new growth on the stubs of where I took cuttings late last summer. When I potted these four plants up in the spring, they did not have a single branch/tip, just the "trunks". They all were of course rooted but the roots were completely dry and brittle after those five months of dormancy.