IMHO MPASM is being neglected to death.
It seems that for years Microchip has acted as if assembly language programming is no longer useful for their controllers.
This point of view is hard to argue with as the vast majority of revenue must be coming from the 16 and 32 bit PIC and Atmel controllers.
With MPLABX the Microchip tools group appears hard pressed to fix the Java craplet bugs in Netbeans that cause it to crash let alone add things to the tools that actually help developers write less buggy code.
Having used the Microchip PIC assembler from when it was first released as something that ran only on PC/MSDOS. I doubt it was much different than the General Instruments assembler it came from.
The changes made to the assembler of over the decades have been extensive but little effort has ever been focused on making it a better assembler for developing code with. To really appreciate what I mean you would need to have used the Intel assembler for the 8086 and the Microchip assembler in the same years. The Intel assembler supported declaration of data structure as complex as anything that a C compiler could do. The Microchip assembler still cannot tell the debugger the size of of the data a symbolic definition references.
There is nothing NOTHING that the Microchip assembler does that actually helps a developer avoid creating buggy code. In almost every way possible the syntax creates situations where bugs are likely, and don't get me started on "warning 302". This was a stupid diagnostic on a PIC16C54 and it only has one bank.
The one and perhaps only thing at present useful about MPASM is the legacy of know good code written with it.
The XC8 assembler (ASPIC) has a different origin. This was one of several target specific assemblers created by Hi-Tech that would accept output from their C compiler for various controllers. Remember back in the day Hi-Tech's business was selling code development tools for a vast array of controller chips.
I suspect that if Hi-Tech was still a going concern today ASPIC would be better and more useful than the GNU assembler.