Which logic families interpret a floating input as a definite value?
This is not a direct answer, but nonetheless relevant information.

While it is true that old TTL would interpret floating inputs as high, this was never something to be relied on in a real design.  The inputs floated only a little above the threshold, so the noise margin was low.  Because they weren't actively driven, the impedance was high.  Between these to affects, floating inputs could, and sometimes did, glitch low.

The usual solution was to pull them to +5 thru 1 k&Omega;.  Sometimes you'd have a unused inverter.  You could ground the input of the inverter, then use its output to hold several unused inputs high.

One way or another, you had to make sure that floating inputs that needed to be interpreted as high were actually held high.  Just leaving them unconnected was irresponsible design, and really did lead to flaky field behavior.