If using 24bits, the computer calculations will be done using 32bit signed integers in its registers, which is faster than with floating point.
Of course coming in and going out will only be at the bit depth of the ADCs and DACs at the most.
However, use any FX and all its calculations will eat into the 24 bits with all the arithmetic rounding. Basic engineering dictates that ALL intermediate calculations MUST be done at higher precision than that required at the end. How much higher is dependent upon the type and number of calculations likely to be encountered.
Many hardware digital mixers internally calculate at 48 or 56 bits, but that could also be to make sure no internal summing points get overloaded, which 32bit floating would NEVER reach practically.
Since 32but floating still only has 24bits of significant binary digits, it provides NO guard bits to prevent calculation rounding affecting the resulting precision, so I support Cubase going to a 64bit internal floating format.
As we use all SSDs, although 64bit files would use twice as much space, there should be plenty of disk performance to spare, so I have no problem supporting the 64bit external floating point as well.
Of course, use of 64bit files in Cubase should just be another one of the file format options.