Weak and strong aren't meaningful terms. A machine ISA might have an inexpressive type system and/or an unsound type system (because it conflates addresses and integers).

> And the reason floating point registers are often separate from integer registers is not to provide this kind of "type safety", it's due to history and architecture.

No, the reason is performance. And we get performance by making statically known distinctions between datatypes, which is what the original poster asked about.

Intermingling the integer and floating point circuitry so they access the same register file would never improve performance over keeping them separate. You'd need longer wires to place them both near the same register files to minimize signal latency, an the added signal delay alone ensures lower performance.