If dropping HT were about security, then why would Intel keep it in their server cores, where security is at least as much of a concern/issue?
This contradicts what AMD
actually did with Zen 5, which was to use a split-decoder design which exclusively benefits SMT. If anything, it seems that AMD is leaning
into SMT, rather than shying away from it.
"Dual decode clusters came up in sideline discussions. The core only uses one of its decode clusters when running a single thread, regardless of whether the sibling thread is idle or SMT is turned off."
The death of Moore's Law has frequently been exaggerated. IMEC has published semiconductor fabrication technology roadmaps reaching into the next decade. There's also ongoing research into new materials. So, I wouldn't bet against there being at least another order of magnitude more performance/efficiency to be found, plus improvements to be made on cost reductions of existing node sizes. Possibly more? Jim Keller has a nice presentation you can find on Youtube explaining why he thinks we're not yet at the end of the road.
Even when we hit a point where virtually no more gains on conventional semiconductors are possible, it's not as if QC must somehow take over from there. It's a different sort of technology that seems to have limited applicability to classical computing. There are ultimately physical limits to everything, even if we're not yet sure exactly where they are.