Yes, I'm sure AMD will be launching their FDSOI K12 derived secret weapon any day now
The Mountain Peak "K12" ARM Core was only ever 16nm TSMC or 14nm GloFo. Any new ARM core, wouldn't be called "K12" but based off another Mountain Peak or completely different naming scheme.
FDSOI projects had no mountain peaks or K-series. The current plan for GloFo's FDSOI is reconfigurable extremely power-efficient "ULP" AMD64 processors. With the first one doing Dynamism with clusters and second one doing Dynamism with grids.
Dynamism = Dynamic Level of Parallelism :: Instruction Level Parallelism associated with OoO and Thread Level Parallelism associated with Multithreading.
Without loss in ILP efficiency or TLP efficiency.
1. ARM custom "Mountain Peak" cores was never FDSOI.
2. FDSOI project developed into aiming at below 4.5W/6W: Micro-family of GF28A Mullins and StoneyX GF28A. With dynamic ILP/TLP without efficiency loss.
TDP Saga:
2014+ - Mullins/Stoney start, the successor planned TDP was 3.6W
2017+ - Removal of Raven2 as G-series and insert of actual G-series successor, with the TDP being ~2W.
=> Client Products have reduced TDP but aren't as low as that.
Process saga:
2012+ - 28FD/20FD
2014+ - Advanced FDSOI
2018+ - Waiting for High Mobility SOI, which was actually suppose to come much, much sooner. This was presented and included into 12FDX in 2015-2016.
2020+ - 12FDX rather than sharing 20nm Lgate with 22FDX, went to sharing 14nm Lgate with 12nm FinFET.
~
ARM Core lineup would have halved AMD's development share between ~50% AMD64 and ~50% ARM64. In hindsight, the trend however would have had the cores split at Zen2.
ARMv8 (Post-K12/2nd Gen Mountain Peak) = VL128
AMD64 (Post-Zen/2nd Gen Zen: Valhalla) = VL256
AMD64 (Post-Zen/3rd Gen Zen: Cerberus) = VL256
AMD64 (Post-Zen/4th Gen Zen: Persephone) = VL512
The inclusion of SVE(purchase of SVE license) would have fixed that, but SVE doesn't perfectly align with AVX2. More issues would largely have popped up trying to keep the cores as similar as possible.
The only benefit of an ARM core is more software developers than AMD64. However, getting developers willing to spend money on getting AMD's custom ARM core is probably like Zen, and not in favor of AMD. Opteron A1100 eventually fell to $399 from $2999. It is unlikely that K12's dev kit would have been cheaper. AMD's development of Mtn. Peaks would have thus be as close as possible to Cortex-A. Where as AMD's development of Zen do to low amount of developers has to copy Intel's P-core. Both of which had a huge generational gap back then.