>>5960674That limitation seems to be a gameplay convention rather than actual incompatibility in the lore, there's no reason you couldn't have a deck and a sandevistan besides eddies and biological limits/humanity loss (these are pretty serious concerns though to be fair). Most people who use one or the other don't have a great deal to benefit from having both - Netrunners aren't often rushing around in the middle of gunfights and Solos don't tend to study the intricacies of programming and Net architecture.
Exceptional individuals can probably be a speedy as fuck techno-battlemage. I doubt they'd be as good at either compared to picking a focus, but that's a hell of nasty combo.