I don't know how widespread or useful (or not) that is, but I installed the big sample libraries like Battery and Kontakt on an external drive, works without problem for me. I suppose there's not a big difference regarding this between Komplete and Komplete 8.
Also make sure, if you want the hard drive + the full variety of instruments, that you purchase Komplete 8 Ultimate. The standard version of Komplete 8 comes without hard drive and has less products included.
I'm upgrading soon as well, still undecsive for which version.
Gear: Analog Keys, JX3P, Nord Electro 3, Mopho Keyboard, Blofeld Keyboard (used as master keyboard only, not as synth), Machinedrum, Mono Lancet, DRM1 MK3, Spark LE, Volca Keys, TAL synths, ValhallaVintageVerb / ÜberMod, Overloud Springage, Fabfilter Pro-Q, Softube Mix Bundle + Trident A-Range, iZotope Ozone, Studio One V2, Faderport, Ableton Live 9, APC 40, Minimonsta, Oddity, U-He Diva, Komplete 9 Ultimate, RME Fireface 400, Zoom R16, Neumann KH 120 A