[Note: Have yet to receive R&M, so framing relative to ACNC and TNA]
Serviceability:
1) Manual w/ blast diagrams (including part numbers), tables listing part numbers w/ details (fastener type/size, etc), trouble shooting guides, etc.
2) Design for easy/quick access to moving parts. E.g., the upper playfield on the shadow is one thumb screw and you're in, whereas getting at the guillotine servo, etc., on ACNC is a PITA.
3) Move away from servos, or use higher quality parts.
Software:
1) Create a partner developer community to assist with software development. (Not necessarily fully open source, but rather a private repo where select individuals can contribute to bug fixes, a Spooky curated list of features, etc.)
Errata:
1) Lock down bars felt "cheap"/sloppy on ACNC and TNA. Hard to engage lock and/or lots of movement OOB. Whereas on JJP and Stern they work well/feel nice OOB.
2) Sharp edges on some exposed parts, like armor, etc.. Haven't noticed this on other manufacturers.