My understanding is that it was a known risk, see the various citations already provided throughout this thread. Meltdown is a bugged design decision because it failed to consider the consequences of asynchronously verifying permission for speculative executions that reach into kernel space, which allows the Spectre attack to affect kernel memory too. That's the limitation of the reach of the "Intel bug" as far as I know, the rest is generally applicable.

The Spectre attack is a side effect of performing speculative execution without wiping caches, something that was, until yesterday, an intentional and clearly-chosen industry design direction, standard across almost every commercial CPU produced in the last 20 years, despite the known risk of "theoretical" timing attacks.

The only reason for Intel to make the decisions that led them to be vulnerable to Meltdown was to sacrifice correctness/safety for performance, and failing to consider the potential side effects of that sacrifice (cache heat). They obviously made a bad risk tradeoff there (though I don't necessarily fault them).

AMD could definitely make the argument that Meltdown was an irresponsible "benchmark cheat" from Intel.

EDIT: And let me further clarify, ARM was "cheating" and doing the permission check asynchronously on some models too (i.e., some of their chips are also vulnerable to Spectre in Kernel-space aka Meltdown). It's not solely an Intel issue.

Speculating memory reference reads across security boundaries is not a trade-off (except if you can prove that you will not further act on them in any data dependant way that is observable). That's mostly common sense.

Spectre does not need that -- but OTOH is more difficult to exploit; it is in a whole different category. There is a reason they have different names.

This seems to be subject to debate...