Fun fact, The Pentium III had an identical pipeline to the Pentium II with added SSE instructions and the Pentium II was just the Pentium Pro pipeline with added MMX instructions. Intel started work on the Pentium Pro back in 1991.
Intel's current architecture is just small incremental improvements to a 27 year old design. The biggest features they have added are Nehalem's hyperthreadding (which they borrowed from Pentium 4) and Sandybridge's uop cache (loop cache).
All their other performance improvements have come from small micro-optimisations and just chucking transistors at the design. Better branch prediction, better load/store buffers, more load/store buffers, more execution units, bigger reorder buffers, wider instruction decoders, more renaming registers, wider instruction retirement, more unique/specialised instructions and of course, clock speed improvements.
But it's still fundamentally the same design which intel could have done back in 1991 if they had the silicon budget.
And this was absolutely the right design decision, everyone else is copying the same design. Apple copied it with their Cyclone/Typhoon/Twister arm CPUs. ARM copied it with their Cortex A57, A72, A73 cpus. AMD copied it with their Zen architecture (after trying out new ideas with Bulldozer and failing). IBM and Sun/Oracle have server class CPUs with more or less the same ideas, but 4 to 8 way "hyperthreadding".
AMD's Zen might pull ahead slightly, but that's only because their design is newer and hopefully free of cobwebs than Intel's design.
But there are still plenty of new CPU design ideas out there, It's quite possible we will see another 50% jump in single threaded performance.