... and bridge designers don't design 'to have fun', but to have structurally sound, cheap and reliable infrastructure tool to cross rivers. Or imagine hiring a construction company for your dream house, realizing only after all is built that they were experimenting and 'having fun' with new unproven materials, construction, wiring etc.

OP's approach is mighty fine for his own endeavors, but if I had such a worker hired, there would be a serious talk about priorities. If no agreement is found even 100x engineer would be let go.

Quantum bridge: its in a superposition of open and closed and will collapse to one of those states when you try to cross. Also its made out of glass and runs on the block chain.

Research engineers do. GP said he is not aiming to build a profitable above all else company. Maximizing fun in a hobby seems legit.

For a hobby and for learning it is absolutely fine. The critique is on businesses running that way fmeither since some developers want to drink the cool-aid on the job or since the company wants to be "attractive" riding the hype train. (How else could they attract the best developers? ;) )

Exactly. Look at Eiffel's Folly, for example.