Yep, the HP42S was the last "great" HP calc. With the "real" 4-level X-Y-Z-T RPN stacks, etc. So natural to use.
A new 42S-II could have flash memory, some clock/timer appointment features, two-way I/O (IR and serial), and 256K of user memory (RAM & ROM). Keep the same form factor.
HP should note: when their used "dead" (no longer mfgd) products sell for as much as or more than their current products (not talking about collectors' items here - these 42S are actually being used!) then something's wrong with the current product line!
Now, it should be possible ("...the exercise is left for the reader..." :-) to take the 42S firmware and do a bit of jimmying with it and put it into the HP49G - plenty of room to add features too. Key labelling would be an issue but at least you'd have at least HP42S functionality.
-Bill