Yes I only can imagine how frustrated he must have felt.
I also understand his decision.
I think that there maybe isn't enough experience made in growing durian out of it's natural environment to tell that it's impossible to make it bloom. Without artificial lighting, constant temperature and humidity it's nearly impossible to grow most of the tropical plants in many parts of Europe. I know that there are many producing cocoa plants for example in greenhouses. So why not Durian if the right conditions where found under greenhouse conditions?
I think in order of exploration and gaining new information it's okay to dream and experiment with that dreams.
To get back to durian, the biggest tree I saw was a Durio zibethinus in the botanical garden of Berlin. It was nearly 3 m (9,8 ft) tall the last time I was there. They also had a giant bread fruit tree that already reached the top of the roof with little fruits on it. So maybe there are more bigger specimens of Durian throughout Europe than one might think. The next time I get there, I will ask if they might know of a durian tree that flowered in other botanical gardens or private collectors they know of. They have a huge greenhouse for tropical fruit plants, I think they are well connected.
I also read that wild jungle durian make the best rootstocks for grafting, since they are well adapted to poor and soggy soil, deseases and stuff. But I guess that counts only for the parts these wild jungle durio are from?
I plan on documenting my growing experience, if they don't make it even through the first winter I save up the money for scions. If they are alive but struggle I have to think about it again. But if they thrive, I will definitely try to get some scions and share all the experiences I made in its own thread.
I also get why you don't want to try growing durian again, all your points are right. Normally I don't grow ultra tropicals, I focus more on dragon fruit, annona, plinia, Eugenia and other smaller shrubs. But I was lucky to try a really good fresh durian a few weeks ago and I fell so in love that I thought that's such nice fruit that I must honor it by growing it as a plant, even if it's just ornamental and not flowering. So I guess I'm becoming that guy that travels just for fresh durian from now on.
I definitely will let you know if my plants survived winter and found a person willing to sell me scions.
And if someone reading this and is willing to support my plan with some D99 or other self compatible durian varieties next year, please feel free to get in contact with me.