But it nonetheless seems a little strange to say -- as Justice Nicholson does here -- that because FELA is a substantive statute with special rules, the applicable rule in state court is not a FELA-specific rule, but rather Rule 68. That's the plain old settlement offer rule, which applies equally to both FELA and non-FELA cases. It may well be that there's, say, a federal common law regarding expert witness fees in FELA cases; i.e., some federal interest advanced by the recovery or non-recovery of such fees that state courts are then bound to apply. But it's difficult for me to believe that Congress intended to incorporate regular old Rule 68 and require state courts to apply that rule (instead of their own) merely because FELA's a federal statute with some unique rules of its own (and yet, none that exist on this issue). That seems different to me.
This reverse Erie stuff is admittedly hard. I wonder, doctrinally, if Justice Nicholson -- as well as his predecessors (Justice Nicholson relies a lot for his holding on Miller, a California case from 2007) is thinking about this the right way. It seems to me to matter whether the procedural rule you're requiring state courts to apply is a generally applicable rule or rather one that's for a particular statute for particular purposes. I agree state courts have to apply federal law in the latter, but am not sure the same's true for the former.
Reverse Erie. That'll get your blood flowing for the weekend, huh?