aiSome random ideas...
SL-5000 and 5500 are similar, dump the 5500(BGA ram I know I've seen mine), use a 5000(SMT ram) and upgrade the RAM from 32mb to 128mb by removing the 32mb's or maybe 32mb to 96mb by piggybacking the originals with larger ones.
For the BGA people(SL-5500, C-xxxx) - How about destroying the existing ram as you remove the BGA chips, making a BGA to smt shim, then soldering wires or SMT chips to the shim. The reason this might be doable, is that my guess is that chip sacrificial removal of the BGA is easier than trying to save it but you'd still be left with the BGA soldering of the shim. After the shim is soldered you'd be able to solder/remove the SMT without damaging the main board. Ie another layer to dissipate heat. Only one risky operation...
Now the 64,000 dollar question.
Why doesn't anyone sell a PDA with more memory? They all max out at 64mb. I know that WinCE does XIP - execute in place. That's where the program can actually run directly from the flash. That gives WinCE a much larger pool of memory for running programs(ie theoretically only heap and stack are in RAM, the rest stays in flash). Linux on the other hand doesn't do XIP(ok so it's being added to 2.6 but it aint there yet). It loads the program code into RAM first before executing.
So we're left with the assumption, more RAM = less battery life. PDA's for average users are all about battery life.
BUT sharp users aren't "average" users. WHY DOESNT SHARP REALIZE 128MB is WORLDS BETTER THAN 64mb.
Sorry about the shouting just dreamed they might actually hear it...
Bill