Itanium tried this and Intel got burnt by the experience. Not saying you’re wrong, just saying Intel won’t believe you for a while yet.
AFAIK Itanium has explicit software control of speculative loads.
We're talking about removing those features, on which our entire computing ecosystem is built, and expecting the compiler to be able to pipeline every execution unit individually.
dex2oat is where the work could be done yes, but we just don't appear to know as a field how to fill in processor pipelines like that - we just don't have that knowledge to do it, and nobody seems to be able to figure it out despite trying several times.
Not universally, even in current-generation devices e.g. the Cortex A53 and A55 are in-order and were explicitly mentioned as safe by ARM.
Snapdragon 625/626 is an octa-core Cortex A53 at 2.2GHz in a lot of the current mid-range devices from almost every major phone manufacturer (Xiaomi, Samsung, Moto, Huawei, Asus, Lenovo, ...)